Testicles

Testicles are male sex organs that are usually in the thick pouch of skin under your penis (scrotum). As part of the male reproductive system, they make sperm and hormones. Most males have two testicles (TES-ti-kuhlz).

There are many different words for testicles. Healthcare providers may use the terms testes (singular “testis”) or gonads. But there are many slang terms for testicles, too. These include balls, cojones and nuts.

What do the testicles do?

Your testicles make two important products. After puberty, they make sperm. Sperm are male reproductive cells. They also make testosterone. Testosterone is a hormone that helps cause many changes during puberty, including:

• Bigger muscles
• Body and facial hair
• A deeper voice
• An increased sex drive
• Larger height

What are the hormones made by the testes?

Your testes make hormones like testosterone in the Leydig cells (interstitial cells). Testes also make:

• Inhibin B: This relates to the size of your testicles (testicular volume). It also relates to the amount of sperm in your semen (sperm count).
• Anti-Müllerian hormone: This is important to the development of your internal reproductive organs.
• Insulin-like factor 3: This hormone helps testicles descend into the scrotum from the abdomen. This is usually shortly before birth. It also helps testicles continue to develop.
• Estradiol: This is important in sperm production.

How do they make sperm?

Your testicles are about 5 degrees Fahrenheit (3 degrees Celsius) lower than the rest of your body. This cooler temperature is better for making sperm (spermatogenesis). In each testicle, spermatogenesis happens in seminiferous tubules. Hormones (like testosterone and follicle-stimulating hormone) stimulate cells in your testicles to develop into sperm.

Where are the testicles located?

Your testicles are in a pouch of skin (scrotum) underneath your penis, between your legs. Most males have one testicle to the right and one to the left in the scrotum.

What are the parts of the testicle?

The parts of the testicle include:

• Tunica: This is a tough connective tissue that covers your testicles. The inner layer is the tunica albuginea. The outer layer is the tunica vaginalis.
• Septa: This includes sections of connective tissue that separate the testicle into lobules.
• Lobules: These are smaller sections of the testicle. Each testicle has about 250 lobules. Each lobule contains between one and four seminiferous tubules.
• Seminiferous tubules: These are tightly coiled tubes that produce sperm. Each testicle has about 700 tubules. They provide blood and nutrients to immature sperm. Areolar tissue fills the spaces between the tubules. Hormone production takes place between the tubules. The coiled tubules meet to form a straight tubule. The straight tubule leads to the rete testis.
• Rete testis: This is a group of small tubes that help move sperm from the testicle to the epididymis.
• Epididymis: This is another type of tube. It runs along the back side of each testicle. It connects to the vas deferens.
• Vas deferens: The vas deferens transports sperm to your urethra before you ejaculate.
• Spermatic cord: Each testicle connects to the inside of your body by a spermatic cord. Each cord contains nerves and blood vessels. The cords also contain the vas deferens.

What do they look like?

You can’t see your testicles because they’re inside your scrotum. But you can see their outlines. You can also feel them. Some describe them as feeling like large olives, small eggs or walnuts.

How big are they?

There’s no exact size for testicles. They’re smaller at birth. They usually stay around the same size until around 8 years old. Then, they start to grow until they reach their adult size during puberty. An adult testicle may range from half an inch (15 mL) to 1.5 inches (35 mL) or more — the size of a bird egg to the size of a small chicken egg.

It’s normal for one of your testicles to be a little bigger than the other. One may hang a little lower, too.

What are the common conditions and disorders that affect the testicles?

Trauma is one of the most common conditions that can affect your testicles. There are no muscles or bones around your testicles to protect them. So, they’re vulnerable to injuries during falls, accidents or roughhousing.

Other conditions that can affect your testicles include:

• Azoospermia: There’s no sperm in your semen.
• Epididymitis: This is inflammation in your epididymis.
• Klinefelter syndrome: This is a genetic condition. At birth, you have an extra copy of the X chromosome.
• Low testosterone (hypogonadism): Your testicles don’t produce enough of the hormones you need.
• Oligospermia: This is a low sperm count.
• Spermatocele: This is when a cyst grows above or behind a testicle.
• Testicular cancer: Testicular cancer is the most common cancer in males between the ages of 20 and 35.
• Testicular torsion: This is when your spermatic cord twists and cuts off your blood supply. Testicular torsion is a medical emergency.
• Undescended testicles (cryptorchidism): Your testicles don’t drop into your scrotum when they should.

Signs or symptoms something isn’t working right

Schedule an appointment with your healthcare provider if you have:

• Blood in your semen (hematospermia)
• Discoloration of your scrotum
• A lump or swelling on your testicle
• Pain in your lower abdomen
• Testicular pain
• Trouble getting your female partner pregnant after over a year of regular unprotected sex
• An unexpected feeling of warmth in the area

What are some ways to care for my testicles?

Testicular self-exams are a great way to learn how your testicles usually look and feel. It’s good practice to check your testicles once a month. If you notice any changes, schedule an appointment with your healthcare provider. It’s also a good idea to have your healthcare provider perform a physical exam of your testicles once a year.

You can also help protect your testicles by:

• Avoiding high temperatures: Limit the amount of time you spend in high temperatures — for example, in saunas or hot tubs.
• Keeping the area clean: Regularly wash your genitals with clean water and soap. Pat the area dry with a clean towel. Regularly change into clean underwear and pants or shorts.
• Practicing safe sex: Use condoms to prevent getting or transmitting sexually transmitted infections (STIs).
• Wearing protection: Wear an athletic supporter (jock strap) if you play contact sports. Examples include baseball, hockey, martial arts, lacrosse or football.

What happens to testicles when ejaculating?

During ejaculation, sperm travel from your testicles to your epididymis. Your epididymis swells a little bit. Sperm then move through your vas deferens and then to your prostate. In your prostate, sperm mix with fluids to create semen. Your vas deferens then squeezes the semen toward the base of your penis. Muscles at the base of your penis contract and force semen out during ejaculation.

Can I get a woman pregnant if I only have one testicle?

Yes, one testicle can produce enough sperm to get your partner pregnant. If healthcare providers must remove both testicles because of cancer or an injury, you may be able to bank your sperm. Sperm banking freezes your sperm so you can use it later to have biological children.