Why is one testicle larger than the other?

Why is one testicle larger than the other?

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Why is one testicle generally larger in humans? Just due to asymmetric development, or is there a hypothesis as to some utility it serves? I read that the different heights may be attributed to attempting to keep them from hitting against one another. Is there a similar guess to the purpose for the difference in sizes?

I would strongly question whether the underlying claim that testicular asymmetry is generally true. While there is no known clinical significance of testicular asymmetry, most men probably have no noticable difference in testicular size. There have been a number of studies over several decades, and findings have been inconsistent.

Braus (1956) stated that the left testis was heavier and lower; Chang et al. (1960) determined on study of cadavers that the right testis was generally larger than the left.

A 2008 study in 0 to 6-year-old boys found no difference in testicular volume measured ultrasonographically.

Age or level of sexual activity may also play a role; it is known that testes get larger during sexual activity.

The reason for testicular asymmetry is unknown. It has been reported in many different species (see Yu, 1998). The most common explanation provided in humans is that the right testis is more commonly larger than the left due to a difference in vascular anatomy: the left testicular vein empties into the renal vein while the right testicular vein empties into the inferior vena cava. However, anatomy alone would not explain testicular asymmetry in other species as well, so there is no doubt more to this than presently understood.

Is it normal to have differently sized testicles?

It is entirely normal for one testicle to be bigger than the other. Many people find that the right testicle is slightly larger and the left hangs lower.

A difference in size is usually nothing to worry about, though it can occasionally indicate a problem. If a testicle is painful or changes shape, a person should see their doctor as soon as possible.

In this article, we look at reasons why one testicle may be bigger than the other. We discuss complications, treatments, and explain how to perform a testicular exam at home.

Share on Pinterest It is common for one testicle to be bigger than the other without a serious cause.

There are several reasons why one testicle may be bigger. These include:


The epididymis is a duct behind the testes. Epididymitis occurs when this duct becomes inflamed, usually as a result of infection. This condition can be a sign of the sexually transmitted infection (STI) chlamydia.

See a doctor if the following symptoms are present:

Orchitis happens when an infection causes inflammation in the testicle. It may occur after a person catches the mumps virus.

If an individual experiences testicular pain and suspects that orchitis is the cause, they should see a doctor. This condition can damage the testicles.

Epididymal cyst

A cyst is a thin sac filled with fluid. Epididymal cysts may occur when there is excess fluid in the duct. They may also form while the epididymis is developing.

These cysts are harmless and usually painless. No treatment is necessary, and they will often go away on their own. If epididymal cysts cause discomfort, however, they can be surgically removed.

A hydrocele

A hydrocele refers to a sac that forms around the testicles and fills with fluid.

While it usually does not require treatment, a hydrocele can indicate inflammation, in which case a person should see a doctor.

A varicocele

When the veins within the scrotum become enlarged, this is called a varicocele.

It usually does not require treatment if there are no additional symptoms, but a varicocele can cause a low sperm count.

Testicular torsion

Testicular torsion occurs when the testicle rotates and the spermatic cord is twisted.

This can cause testicular pain that is severe and lasting. If this pain follows an injury, it may subside then suddenly return.

Testicular torsion is severe and should be treated as an emergency. The twisting of the cord can reduce or block blood flow to the testicle, and without treatment the testicle may need to be removed.

Testicular cancer

Cancerous cells can appear and multiply in the testicle. A doctor should investigate lumps or new growths in the area as soon as possible.

According to the American Cancer Society, testicular cancer is uncommon, developing in about 1 in 250 males. It is most prevalent in young and middle-aged men and can usually be treated successfully.

Several signs and symptoms can indicate a problem with testicular health.

If any of the following symptoms occur with an enlarged testicle, seek medical attention as soon as possible:

  • a sharp pain or ache in or around the testicles
  • swelling of the testicles
  • redness
  • discharge from the penis
  • trouble passing urine
  • pain in the back or lower abdomen
  • swelling or tenderness in the breast tissue

A doctor will help to identify the underlying cause by examining the scrotum and testicles for lumps or abnormalities. If they suspect testicular cancer, they will take a blood test and ask about family history.

Other tests a doctor may recommend include:

  • a urine test to check for infections and kidney problems
  • an ultrasound to look for growths and check blood flow
  • a CT scan to look for testicular abnormalities

If an underlying condition is diagnosed, a doctor may prescribe medication or other treatment.

Treatment for differently sized testicles depends on the cause. Below are common underlying conditions and their treatments.

Epididymitis. If chlamydia is the cause of epididymitis, a doctor will usually prescribe a course of antibiotics to treat the infection, and may recommend elevating the scrotum to reduce swelling.

Orchitis. If an STI is causing orchitis, a doctor will usually prescribe medication to fight the infection. Common medications include ceftriaxone (Rocephin) or azithromycin (Zithromax). Painkillers and an ice pack may help to relieve discomfort.

Testicular torsion. Testicular torsion requires treatment as soon as possible. A doctor may be able to untwist the testicle, in a procedure called manual detorsion, but surgery is often necessary to prevent reoccurrence. A delay in treatment increases the likelihood that the twisted testicle will need to be removed.

Testicular cancer. A doctor may recommend removing the testicle where the cancer is present. Radiation therapy , chemotherapy, or a combination may help to reduce or destroy cancer cells. If the cancer has spread, or if it originated in another part of the body, additional treatments and surgeries may be necessary.

It is very important to monitor the size and shape of testicles so that any change can be detected.

Perform a self-examination once a month. Be on the lookout for lumps, growths, pain, swelling, and other abnormalities.

A healthy testicle is smooth, and closer to egg-shaped than round. Lumps or abnormal protrusions should be investigated by a doctor right away.

To perform a testicular self-exam:

  • Ensure that the scrotum is loose before beginning.
  • Carefully and slowly roll the testicle between the fingers and thumb.
  • Thoroughly check the surface of each testicle, looking for lumps, areas that feel tender or sore, protrusions, swelling, or changes in size.
  • Feel along the bottom of the scrotum, reaching the epididymis, which should feel like several grouped tubes.

Check both testicles at least once a month.

Having differently sized testicles is common.

If one testicle becomes noticeably bigger, most underlying causes are easily treated. The sooner a person consults a doctor, the better the outlook is likely to be.

If other symptoms are present, such as pain, lumps, or swelling, seek medical attention right away.

While a diagnosis of cancer is concerning, the outlook for testicular cancer is good. Treatment and support can help a person and their family to deal with this condition.

One Testicle Larger Than the Other in Toddler: A Case of Undescended Testicles

Undescended testes is actually a common condition, occurring in one out of a hundred newborn baby boys. Mums who give birth to baby boys may recognise the condition when their newborn sons appear to have one or both testicles missing from their scrotum.

This odd condition happens because the testicle doesn’t grow outside. Rather, it develops in the abdomen first while the baby is still in the womb. Undescended testicles happen when the testicle doesn’t properly grow out of the body – leaving baby boys with only one or no testicles at all.

Approximately 50% of all affected newborn baby boys will have their testicles “descend” into their scrotums. Others might be a couple of months behind schedule. But for babies whose testicles don’t descend at all, it could spell increased risks of other serious issues as they grow up.

Now a new study led by University of Sydney researchers has warned that delaying surgery to fix the problem can put boys at heightened risk of serious health problems as they grow into adulthood.

9 Weird Facts About Testicles Every Woman Needs to Know

Be honest: Have you ever wondered what it really feels like to get kicked in the balls? Some dudes compare it to the pain of giving birth (um, no), while others say it&aposs more like getting punched in the stomach by a professional boxer.

We&aposll never know for sure, but that doesn&apost mean we&aposre not curious about other testicle mysteries. For example, why does one hang lower than the other? And what are "blue balls," anyway? To get answers, we spoke to a doctor who specializes in male sexuality. These nine family jewels facts will blow your mind—or make you glad you don&apost have a pair dangling between your legs.

Testicles are sperm factories

The testicles, also called the testes, produce about 1,500 sperm every second, Michael Reitano, MD, physician-in-residence at men’s health company Roman, tells Health. That&aposs about 90,000 sperm every minute, 5.4 million every hour, and 130 million every day. Each guy is different, and sperm count does vary, but the typical pair of nuts make well over a million sperm every. single. day.

It only takes one sperm to fertilize a woman&aposs egg, but the average ejaculation (which clocks in at about one-half to one teaspoon of semen) contains anywhere from 40 to 130 million sperm, Dr. Reitano says. If sperm isn&apost released through ejaculation, it&aposs simply reabsorbed back into the body.

They're 5 degrees colder than the rest of the body

"If you think about it, the female has gonads as well, the ovaries, but why are they so well protected inside of the body when the male gonads are outside of the body and so vulnerable?" Dr. Reitano asks. The answer? Testicular temperature has to be about 5 degrees lower than the rest of the body in order to properly preserve sperm. The scrotum (the wrinkly pouch of skin that holds the testicles) is about 93.4 degrees Fahrenheit, while the body is typically 98.6.

The muscles in the scrotum actually act as temperature control for the testicles by moving them closer to or farther away from the body as the air gets warmer or cooler. For example, when the testicles get a bit too chilly, the scrotum will contract and pull them closer to the body for warmth. And if they can&apost take the heat, the scrotum will relax and let the testes hang low.

One hangs lower for a reason

The testicle on the left usually hangs a little lower than the one on the right, and it&aposs no accident. "This allows the temperature of one testis to change without that energy being sent to the other testis, as it would if they were adjacent or touching," Dr. Reitano says. This way, the body can increase or decrease the temperature of one testis without affecting the temperature of the other. Now that&aposs the kind of advanced heating/cooling system needed in just about every office building ever.

It&aposs also normal for one to be a little bigger than the other. You know, just like boobs. Dr. Reitano says the right tends to be larger than the left.

They hurt like hell when they get hit

Okay, let&aposs look at the facts: The testicles are crucial to reproduction, but unlike the ovaries, they&aposre super vulnerable because they hang outside of the body. So how does nature protect them? Dr. Reitano explains that the testicles evolved to have a ton of nerves that are crazy sensitive to pain because this makes guys way more likely to protect them in case of danger.

The muscles in the scrotum will also pull the testes closer to the body if they sense any kind of danger. even if it&aposs not always actual danger. Dr. Reitano says if you stroke your guy&aposs inner thigh, you&aposll probably notice his scrotum brings the testicles nearer to his body. That reflex can also respond to emotions. "If a man feels threatened or fear, the muscles will [contract] without him even being aware of it," he adds..

The scrotum is as sexually sensitive as your vulva

We know the testicles are extremely pain-receptive, but they themselves aren&apost as sensitive to sexual pleasure as you might think. It&aposs actually the scrotal sac, which holds the testicles, that&aposs an erogenous zone. "The scrotum corresponds to the vulva and labia in females," says Dr. Reitano, putting it in perspective. There&aposs no way to be 100% sure how similar the sensation is, but "we can estimate that the sensations are fairly similar in that we know the nerve distribution is almost identical," he adds. Playing with his scrotum alone probably won&apost make him orgasm. but it still feels pretty damn good.

Tight-fitting underwear takes a toll

A study published last year in Human Reproduction found that men who primarily wore boxer shorts averaged 25% higher sperm concentration and 17% higher total sperm count than men who wore other types of underwear. Dr. Reitano says he recommends loose fitting underwear (e.g. boxers) because it gives the testicles enough space to regulate temperature by moving closer to or farther away from the body. Sitting too long in a hot tub can also cause similar sperm count problems, since excess heat degrades sperm quality.

Testicular cancer is often caught late

Signs of testicular cancer include achiness or pain in a guy&aposs back, groin, belly, or scrotum abdominal bloating a heavy feeling in his scrotum a change in size of one or both testicles or a lump on the testicles. Unfortunately, testicular tumors are often caught late because they can grow without compressing any other organs or bones nearby, making them relatively painless, Dr. Reitano says. The skin of the scrotum is so loose that a testicular tumor can grow without constraint.

Luckily, testicular cancer is highly curable, but it&aposs still very important for guys to do self-examinations. (It&aposs most common in men between ages 15 and 35, just FYI.) You can help him by taking matters into your own hands, literally. “Gently roll the testicle between the thumb and one or two fingers, and feel for a symmetric, round structure,” Michael A. Palese MD, chair of urology at Mount Sinai Downtown-Union Square in New York City, previously told Health. You want everything to feel "homogenous," he said, with no lumps or bumps.

One sometimes hides in a guy's body

When a boy baby is developing in the womb, his testicles typically drop from the abdomen to the scrotum. But in some cases, a newborn comes into the world with one or both testicles still in his abdomen. Sometimes the testicles will drop on their own in the first few months of life, but if it hasn&apost happened by the four-month mark, surgery will probably be needed, according to Mayo Clinic.

Though surgery can easily resolve the problem, it carries a risk of complications later in life. Dr. Reitano says men born with undescended testicles are 40 times more likely to develop testicular cancer. Risk factors for having a baby with hidden jewels include premature birth, low birth weight, family history of undescended testicles, and alcohol or cigarette use by the mother during pregnancy, according to Mayo Clinic.

Balls don't actually turn blue&mdashbut they can double in size

Men use the term "blue balls" to describe the painful aching they feel in their testicles when they become very aroused but don&apost get any release. Sure it&aposs unpleasant, but we&aposre not talking severe pain here. it shouldn&apost be anything more than mildly uncomfortable (for all the drama kings out there).

The medical term for blue balls is epididymal hypertension (EH), and it happens when the blood vessels to the penis and testicles expand to make room for increased blood flow, Dr. Reitano says, which is how a man gets an erection. (His penis isn&apost the only thing that grows when a guy is turned on. his balls also can double in size, seriously.) The blood flow subsides after an orgasm, but if orgasm doesn&apost happen, he&aposll just have to wait for it to decrease. which is where the discomfort comes in.

One of my testicles feels bigger than the other after my vasectomy. Is this normal?

The operative word in this question is "feels." If a man has the sensation that a testicle is swollen there are a couple of scenarios. It may be indeed swollen and this could be a hematoma (collection of blood) or an infection most probably epididymits. The former no treatment is necessary in the latter you'd need to see your doctor for an antibiotic. Having said this the most common reason for the sensation that a testicle is bigger is not that it is bigger but due to the changes that occur after a vasectomy the testicle "feels" bigger. In the shower you can easily feel and compare the testicles and if they measure out about the same then it confirms this point. As with anything of concern the default action is to see your urologist. This visit if you make it is usually done at no cost to you as it is commonly covered by the initial cost of the vasectomy.

The operative word in this question is "feels." If a man has the sensation that a testicle is swollen there are a couple of scenarios. It may be indeed swollen and this could be a hematoma (collection of blood) or an infection most probably epididymits. The former no treatment is necessary in the latter you'd need to see your doctor for an antibiotic. Having said this the most common reason for the sensation that a testicle is bigger is not that it is bigger but due to the changes that occur after a vasectomy the testicle "feels" bigger. In the shower you can easily feel and compare the testicles and if they measure out about the same then it confirms this point. As with anything of concern the default action is to see your urologist. This visit if you make it is usually done at no cost to you as it is commonly covered by the initial cost of the vasectomy.

Causes of Swollen Left Testicle with No Pain

Some of the reasons of painless testicular swelling of left side are:

  • Due to descending hernia which may be retractable or non retractable, in retractable hernia the swelling subside in lying down position
  • Hydrocele is one o the most common cause of painless swelling of testis, it is due to the accumulation of fluid in between two membranes of the testis, it is palpable and fluctuating
  • Varicocele is also one of the painless conditions of swollen testicle.

Investigation advised: Ultrasound of testis, color dopler study of testicular vein.

If hernia is present, there may be swelling in the inguinal region with testicular swelling


Males have two testicles of similar size contained within the scrotum, which is an extension of the abdominal wall. Scrotal asymmetry is not unusual: one testicle extends farther down into the scrotum than the other due to differences in the anatomy of the vasculature.


The volume of the testicle can be estimated by palpating it and comparing it to ellipsoids of known sizes. Another method is to use calipers (an orchidometer) or a ruler either on the person or on an ultrasound image to obtain the three measurements of the x, y, and z axes (length, depth and width). These measurements can then be used to calculate the volume, using the formula for the volume of an ellipsoid:

An average adult testicle measures up to 5 cm × 2 cm × 3 cm (2 in × 3 ⁄ 4 in × 1 + 1 ⁄ 4 in). The Tanner scale for the maturity of male genitals assigns a maturity stage to the calculated volume ranging from stage I, a volume of less than 1.5 cm 3 to stage V, a volume greater than 20 cm 3 . Normal volume is 15 to 25 cm 3 the average is 18 cm 3 per testis (range 12–30 cm 3 ). [1]

Internal structure

Duct system

The testes are covered by a tough membranous shell called the tunica albuginea. Within the testes are very fine coiled tubes called seminiferous tubules. The tubules are lined with a layer of cells (germ cells) that develop from puberty through old age into sperm cells (also known as spermatozoa or male gametes). The developing sperm travel through the seminiferous tubules to the rete testis located in the mediastinum testis, to the efferent ducts, and then to the epididymis where newly created sperm cells mature (see spermatogenesis). The sperm move into the vas deferens, and are eventually expelled through the urethra and out of the urethral orifice through muscular contractions.

Primary cell types

  • Here, germ cells develop into spermatogonia, spermatocytes, spermatids and spermatozoon through the process of spermatogenesis. The gametes contain DNA for fertilization of an ovum [2] – the true epithelium of the seminiferous epithelium, critical for the support of germ cell development into spermatozoa. Sertoli cells secrete inhibin. [3] surround the seminiferous tubules. [4]
    – cells localized between seminiferous tubules that produce and secrete testosterone and other androgens important for sexual development and puberty, secondary sexual characteristics like facial hair, sexual behavior and libido, supporting spermatogenesis and erectile function. Testosterone also controls testicular volume.
  • Also present are:
    • Immature Leydig cells
    • Interstitial macrophages and epithelial cells.

    Blood supply and lymphatic drainage

    Blood supply and lymphatic drainage of the testes and scrotum are distinct:

    • The paired testicular arteries arise directly from the abdominal aorta and descend through the inguinal canal, while the scrotum and the rest of the external genitalia is supplied by the internal pudendal artery (itself a branch of the internal iliac artery).
    • The testis has collateral blood supply from 1. the cremasteric artery (a branch of the inferior epigastric artery, which is a branch of the external iliac artery), and 2. the artery to the ductus deferens (a branch of the inferior vesical artery, which is a branch of the internal iliac artery). Therefore, if the testicular artery is ligated, e.g., during a Fowler-Stevens orchiopexy for a high undescended testis, the testis will usually survive on these other blood supplies.
    • Lymphatic drainage of the testes follows the testicular arteries back to the paraaortic lymph nodes, while lymph from the scrotum drains to the inguinal lymph nodes.


    Many anatomical features of the adult testis reflect its developmental origin in the abdomen. The layers of tissue enclosing each testicle are derived from the layers of the anterior abdominal wall. Notably, the cremasteric muscle arises from the internal oblique muscle.

    The blood–testis barrier

    Large molecules cannot pass from the blood into the lumen of a seminiferous tubule due to the presence of tight junctions between adjacent Sertoli cells. The spermatogonia are in the basal compartment (deep to the level of the tight junctions) and the more mature forms such as primary and secondary spermatocytes and spermatids are in the adluminal compartment.

    The function of the blood–testis barrier may be to prevent an auto-immune reaction. Mature sperm (and their antigens) arise long after immune tolerance is established in infancy. Therefore, since sperm are antigenically different from self tissue, a male animal can react immunologically to his own sperm. In fact, he is capable of making antibodies against them.

    Injection of sperm antigens causes inflammation of the testis (auto-immune orchitis) and reduced fertility. Thus, the blood–testis barrier may reduce the likelihood that sperm proteins will induce an immune response, reducing fertility and so progeny.

    Temperature regulation

    Spermatogenesis is enhanced at temperatures slightly less than core body temperature. [5] The spermatogenesis is less efficient at lower and higher temperatures than 33 °C. [5] Because the testes are located outside the body, the smooth tissue of the scrotum can move them closer or further away from the body. [5] The temperature of the testes is maintained at 35 degrees Celsius (95 degrees Fahrenheit), i.e. two degrees below the body temperature of 37 degrees Celsius (98.6 degrees Fahrenheit). Higher temperatures affect spermatogenesis. [6] There are a number of mechanisms to maintain the testes at the optimum temperature. [5]

    The cremasteric muscle is part of the spermatic cord. When this muscle contracts, the cord is shortened and the testicle is moved closer up toward the body, which provides slightly more warmth to maintain optimal testicular temperature. When cooling is required, the cremasteric muscle relaxes and the testicle is lowered away from the warm body and is able to cool. Contraction also occurs in response to stress (the testicles rise up toward the body in an effort to protect them in a fight).

    The cremaster muscle can reflexively raise each testicle individually if properly triggered. This phenomenon is known as the cremasteric reflex. The testicles can also be lifted voluntarily using the pubococcygeus muscle, which partially activates related muscles.

    Gene and protein expression

    The human genome includes approximately 20,000 protein coding genes: 80% of these genes are expressed in adult testes. [7] The testes have the highest fraction of tissue type-specific genes compared to other organs and tissues: [8] about 1000 of them are highly specific for the testes, [7] and about 2,200 show an elevated pattern of expression here. A majority of these genes encode for proteins that are expressed in the seminiferous tubules and have functions related to spermatogenesis. [9] [8] Sperm cells express proteins that result in the development of flagella these same proteins are expressed in the female in cells lining the fallopian tube, and cause the development of cilia. In other words, sperm cell flagella and Fallopian tube cilia are homologous structures. The testis-specific proteins that show the highest level of expression are protamines.

    There are two phases in which the testes grow substantially namely in embryonic and pubertal age.


    During mammalian development, the gonads are at first capable of becoming either ovaries or testes. [10] In humans, starting at about week 4 the gonadal rudiments are present within the intermediate mesoderm adjacent to the developing kidneys. At about week 6, sex cords develop within the forming testes. These are made up of early Sertoli cells that surround and nurture the germ cells that migrate into the gonads shortly before sex determination begins. In males, the sex-specific gene SRY that is found on the Y-chromosome initiates sex determination by downstream regulation of sex-determining factors, (such as GATA4, SOX9 and AMH), which leads to development of the male phenotype, including directing development of the early bipotential gonad down the male path of development.

    Testes follow the "path of descent" from high in the posterior fetal abdomen to the inguinal ring and beyond to the inguinal canal and into the scrotum. In most cases (97% full-term, 70% preterm), both testes have descended by birth. In most other cases, only one testis fails to descend (cryptorchidism) and that will probably express itself within a year.


    The testes grow in response to the start of spermatogenesis. Size depends on lytic function, sperm production (amount of spermatogenesis present in testis), interstitial fluid, and Sertoli cell fluid production. After puberty, the volume of the testes can be increased by over 500% as compared to the pre-pubertal size. [ citation needed ] Testicles are fully descended before one reaches puberty.

    Protection and injury

    • The testicles are well known to be very sensitive to impact and injury. The pain involved travels up from each testicle into the abdominal cavity, via the spermatic plexus, which is the primary nerve of each testicle. This will cause pain in the hip and the back. The pain usually goes away in a few minutes. is a medical emergency. is a medical emergency caused by blunt force impact, sharp edge, or piercing impact to one or both testicles, which can lead to necrosis of the testis in as little as 30 minutes. [citation needed]
    • Penetrating injuries to the scrotum may cause castration, or physical separation or destruction of the testes, possibly along with part or all of the penis, which results in total sterility if the testicles are not reattached quickly.
    • Some jockstraps are designed to provide support to the testicles. [11]

    Diseases and conditions

      and other neoplasms – To improve the chances of catching possible cases of testicular cancer or other health issues early, regular testicular self-examination is recommended. , swollen vein(s) from the testes, usually affecting the left side, [12] the testis usually being normal , swelling around testes caused by accumulation of clear liquid within a membranous sac, the testis usually being normal , a retention cyst of a tubule of the rete testis or the head of the epididymis distended with barely watery fluid that contains spermatozoa can also affect the size and function of the testis.
  • Certain inherited conditions involving mutations in key developmental genes also impair testicular descent, resulting in abdominal or inguinal testes which remain nonfunctional and may become cancerous. Other genetic conditions can result in the loss of the Wolffian ducts and allow for the persistence of Müllerian ducts. Both excess and deficient levels of estrogens can disrupt spermatogenesis and cause infertility. [13] is a deformity in which the testicle is not attached to the scrotal walls, and can rotate freely on the spermatic cord within the tunica vaginalis. It is the most common underlying cause of testicular torsion. inflammation of the testicles , a painful inflammation of the epididymis or epididymides frequently caused by bacterial infection but sometimes of unknown origin. , the absence of one or both testicles. or "undescended testicles", when the testicle does not descend into the scrotum of the infant boy.
  • Testicular enlargement is an unspecific sign of various testicular diseases, and can be defined as a testicular size of more than 5 cm (long axis) x 3 cm (short axis). [14]

    Blue balls is a slang term for a temporary fluid congestion in the testicles and prostate region caused by prolonged sexual arousal.

    Testicular prostheses are available to mimic the appearance and feel of one or both testicles, when absent as from injury or as treatment in association to gender dysphoria. There have also been some instances of their implantation in dogs. [15]

    Effects of exogenous hormones

    To some extent, it is possible to change testicular size. Short of direct injury or subjecting them to adverse conditions, e.g., higher temperature than they are normally accustomed to, they can be shrunk by competing against their intrinsic hormonal function through the use of externally administered steroidal hormones. Steroids taken for muscle enhancement (especially anabolic steroids) often have the undesired side effect of testicular shrinkage.

    Similarly, stimulation of testicular functions via gonadotropic-like hormones may enlarge their size. Testes may shrink or atrophy during hormone replacement therapy or through chemical castration.

    In all cases, the loss in testes volume corresponds with a loss of spermatogenesis.

    Testicles of a male calf or other livestock are cooked and eaten in a dish sometimes called Rocky Mountain oysters. [16]

    As early as 330 BC, Aristotle prescribed the ligation (tying off) of the left testicle in men wishing to have boys. [17] In the Middle Ages, men who wanted a boy sometimes had their left testicle removed. This was because people believed that the right testicle made "boy" sperm and the left made "girl" sperm. [18]

    One theory about the etymology of the word testis is based on Roman law. The original Latin word testis, "witness", was used in the firmly established legal principle "Testis unus, testis nullus" (one witness [equals] no witness), meaning that testimony by any one person in court was to be disregarded unless corroborated by the testimony of at least another. This led to the common practice of producing two witnesses, bribed to testify the same way in cases of lawsuits with ulterior motives. Since such "witnesses" always came in pairs, the meaning was accordingly extended, often in the diminutive (testiculus, testiculi). [ citation needed ]

    Another theory says that testis is influenced by a loan translation, from Greek parastatēs "defender (in law), supporter" that is "two glands side by side". [19]

    In slang, the testes are usually referred to as "balls" as a reference to blue balls. Frequently, "nuts" (sometimes intentionally misspelled as "nutz") are also a slang term for the testes due to the geometric resemblance., as evidenced by the various usages of the term "Deez Nuts", which include a satirical political candidate in 2016.

    External appearance

    In sharks, the testicle on the right side is usually larger, and in many bird and mammal species, the left may be the larger. The primitive jawless fish have only a single testis, located in the midline of the body, although even this forms from the fusion of paired structures in the embryo. [20]

    In seasonal breeders, the weight of the testes often increases during the breeding season. [21] The testicles of a dromedary camel are 7–10 cm (2.8–3.9 in) long, 4.5 cm (1.8 in) deep and 5 cm (2.0 in) in width. The right testicle is often smaller than the left. [22]



    The basal condition for mammals is to have internal testes. [23] The testes of monotremes, [24] [25] xenarthrans, [25] and elephants [26] remain within the abdomen. There are also some marsupials with external testes [27] [28] [29] and Boreoeutherian mammals with internal testes, such as the rhinoceros. [30] Cetaceans such as whales and dolphins also have internal testes. [31] [32] As external testes would increase drag in the water they have internal testes which are kept cool by special circulatory systems that cool the arterial blood going to the testes by placing the arteries near veins bringing cooled venous blood from the skin. [33] [34] In odobenids and phocids, the location of the testes is para-abdominal, though otariids have scrotal testes. [35]


    Boreoeutherian land mammals, the large group of mammals that includes humans, have externalized testes. [36] Their testes function best at temperatures lower than their core body temperature. Their testes are located outside of the body, suspended by the spermatic cord within the scrotum.

    There are several hypotheses why most boreotherian mammals have external testes which operate best at a temperature that is slightly less than the core body temperature, e.g. that it is stuck with enzymes evolved in a colder temperature due to external testes evolving for different reasons, that the lower temperature of the testes simply is more efficient for sperm production.

    1) More efficient. The classic hypothesis is that cooler temperature of the testes allows for more efficient fertile spermatogenesis. In other words, there are no possible enzymes operating at normal core body temperature that are as efficient as the ones evolved, at least none appearing in our evolution so far.

    The early mammals had lower body temperatures and thus their testes worked efficiently within their body. However it is argued that boreotherian mammals have higher body temperatures than the other mammals and had to develop external testes to keep them cool. It is argued that those mammals with internal testes, such as the monotremes, armadillos, sloths, elephants, and rhinoceroses, have a lower core body temperatures than those mammals with external testes. [ citation needed ]

    However, the question remains why birds despite having very high core body temperatures have internal testes and did not evolve external testes. [37] It was once theorized that birds used their air sacs to cool the testes internally, but later studies revealed that birds' testes are able to function at core body temperature. [37]

    Some mammals which have seasonal breeding cycles keep their testes internal until the breeding season at which point their testes descend and increase in size and become external. [38]

    2) Irreversible adaptation to sperm competition. It has been suggested that the ancestor of the boreoeutherian mammals was a small mammal that required very large testes (perhaps rather like those of a hamster) for sperm competition and thus had to place its testes outside the body. [39] This led to enzymes involved in spermatogenesis, spermatogenic DNA polymerase beta and recombinase activities evolving a unique temperature optimum, slightly less than core body temperature. When the boreoeutherian mammals then diversified into forms that were larger and/or did not require intense sperm competition they still produced enzymes that operated best at cooler temperatures and had to keep their testes outside the body. This position is made less parsimonious by the fact that the kangaroo, a non-boreoeutherian mammal, has external testicles. The ancestors of kangaroos might, separately from boreotherian mammals, have also been subject to heavy sperm competition and thus developed external testes, however, kangaroo external testes are suggestive of a possible adaptive function for external testes in large animals.

    3) Protection from abdominal cavity pressure changes. One argument for the evolution of external testes is that it protects the testes from abdominal cavity pressure changes caused by jumping and galloping. [40]

    4) Protection against DNA damage. Mild, transient scrotal heat stress causes DNA damage, reduced fertility and abnormal embryonic development in mice. [41] DNA strand breaks were found in spermatocytes recovered from testicles subjected to 40 °C or 42 °C for 30 minutes. [41] These findings suggest that the external location of the testicles provides the adaptive benefit of protecting spermatogenic cells from heat-induced DNA damage that could otherwise lead to infertility and germline mutation.

    The relative size of testes is often influenced by mating systems. [42] Testicular size as a proportion of body weight varies widely. In the mammalian kingdom, there is a tendency for testicular size to correspond with multiple mates (e.g., harems, polygamy). Production of testicular output sperm and spermatic fluid is also larger in polygamous animals, possibly a spermatogenic competition for survival. The testes of the right whale are likely to be the largest of any animal, each weighing around 500 kg (1,100 lb). [43]

    Among the Hominidae, gorillas have little female promiscuity and sperm competition and the testes are small compared to body weight (0.03%). Chimpanzees have high promiscuity and large testes compared to body weight (0.3%). Human testicular size falls between these extremes (0.08%). [44]

    Testis weight also varies in seasonal breeders like red foxes, [45] golden jackals [46] and coyotes. [21]

    Internal structure

    Under a tough membranous shell called the tunica albuginea, the testis of amniotes, as well as some teleost fish, contains very fine coiled tubes called seminiferous tubules.

    Amphibians and most fish do not possess seminiferous tubules. Instead, the sperm are produced in spherical structures called sperm ampullae. These are seasonal structures, releasing their contents during the breeding season, and then being reabsorbed by the body. Before the next breeding season, new sperm ampullae begin to form and ripen. The ampullae are otherwise essentially identical to the seminiferous tubules in higher vertebrates, including the same range of cell types. [20]

    My testicles have changed size

    Seven years ago my testicles seemed to change in size. The left testicle has totally shrunk in size while the other has increased considerably in size.

    I have never experienced any pain or problems with ejaculation, going to the toilet, etc.

    You may find it strange that I have never had this checked out, but as I say this has not caused me any pain or problems in use whatsoever.

    I am still a virgin so the issue has not been discussed with a partner. Can you please advise what it might be? I obviously realise I should see a GP as soon as possible to get it looked at.

    The reason I am suddenly concerned about this now is because I am now in a relationship that may well progress further sexually and do not want to cause any embarrassment on either side.

    A reply with any suggestions would be appreciated.

    Please do not think this is a hoax, I am of a very shy nature and a visit to the doctor petrifies me, probably more than most, particularly as I have continuously left it for several years.


    As a fellow male I fully understand your sentiments, but hope that my explanation and reassurance will persuade you otherwise.

    The trouble with us men is that we are reluctant to go to a doctor for advice and/or an examination when we need to and often need to be dragged kicking and screaming!

    No-one anatomically speaking is completely symmetrical. This is especially true for men in the testicular department.

    One testicle is usually larger or smaller than the other, they hang at different angles and one is often lower or higher than its counterpart too.

    The only way to ensure all is well and to put your mind at rest is to have an examination, and to assist you I will describe what is likely to happen.

    Your doctor will ask you how long you have had the size difference for and how they have changed over time, and enquire about any associated symptoms, such as fever, rash, testicular pain, or discharge from the penis.

    The fact that you have not experienced any of these symptoms is very encouraging.

    If this is the case, and they are not causing you any problems except worry, it is unlikely that you will require any further tests and your doctor will be able to reassure you.

    Occasionally, the doctor will want to clarify the diagnosis with a blood test or an ultrasound scan of the scrotum (at the local hospital), but this is not usually necessary and most of the time a simple examination by your GP is all that is required to find out the cause of your concern.

    Right testicle bigger than left.

    Hello im 24. My right testicle is bigger and higher than the left testicle. I took a picture of my testicles and drew them on the computer, size differences appear below. I did not feel any lump when I touched it. I feel epididymis both of my testicles and feel same. Also i don't have any pain. Should i be worried and go to doctor? Or is the size difference normal?

    Photo is safe, it's just 2 oval shapes.

    Okay, so we really need a FAQ or significantly better anatomy lessons, particularly for boys.

    Balls are almost NEVER perfectly symmetrical. One almost always hangs lower and the sizes are basically never exactly the same one will always be bigger or smaller than the other. That's normal.

    In doing your self-examination, did you feel a bunch of lumps or stringy, wormy veins in your sack? Because if you did, you need to get an Ultrasound. If you didn't, you're fine please relax.

    My one right testicle is very small and right one is very big, and it also causes pain in the left part of my stomach. What I should do?

    Posted January 9, 2019 under Ask Us.
    +Related Content

    Thank you for your question, it’s always a good idea to ask questions when you notice changes in your body or things you find concerning!

    It is not unusual for most young men to have one testicle that is slightly larger than the other however, if you notice a major difference in size, especially if it’s a change from before, you should see your health care provider right away. Changes in apparent size of your testicle and one-sided stomach pain can be caused by a hernia, where part of your intestine pushes its way through a small hole in the abdominal wall into the scrotum (sometimes from heavy weight-lifting) or it could indicate a problem with your blood flow involving the veins of your scrotum. But it is very difficult to know the specific cause (without a thorough evaluation), which is why it’s important that you see a medical provider. Tell them about the pain, the location, when you first noticed it, how it feels­, how often you have it, what makes it worse and what helps to relieve it. It’s also important to tell your provider if you are sexually active. Your provider will likely examine you and ask additional questions to ensure the right diagnosis is made to recommend the appropriate treatment and help you to start feeling better!

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