Testicles

The testicles (also called testes) are two oval-shaped glands that sit inside the scrotum. They have two jobs: producing sperm and producing testosterone (the hormone that drives puberty and sexual development in people with testes). They're sometimes called "balls" or "bollocks."

• The testicles produce sperm and testosterone.
• They sit inside the scrotum, outside the body, because sperm need a slightly cooler temperature to develop.
• It's completely normal for one to be slightly larger or hang lower than the other.
• They develop and grow during puberty.
• Checking your testicles regularly for lumps or changes is a good habit — testicular cancer is rare in young people but very treatable when caught early.

What they do

Sperm production — the testicles produce millions of sperm per day from puberty onwards. This happens continuously throughout life. The sperm mature in a coiled tube called the epididymis, which sits behind each testicle, before travelling through the vas deferens during ejaculation.

Testosterone production — the testicles produce testosterone, which is responsible for puberty changes like voice deepening, body and facial hair, muscle development, and increased sex drive. Testosterone continues to play a role in sexual function, energy, and mood throughout life.

Size and symmetry

Testicles vary in size from person to person — like any body part. One is almost always slightly bigger or hangs lower than the other (usually the left). This is normal and stops them squashing together. During puberty, the testicles grow significantly — this is usually one of the first signs of puberty, though it's less obvious than other changes.

Checking them

Getting into the habit of checking your testicles occasionally is genuinely worthwhile. Testicular cancer is one of the most common cancers in young men (ages 15-35), but it's also one of the most treatable — especially when caught early. [CHECK: current UK incidence age range]

Check after a warm bath or shower when the scrotum is relaxed. Gently roll each testicle between your thumb and fingers, feeling for any hard lumps, swelling, or changes in size. A small, soft tube at the back (the epididymis) is normal. Any new hard lumps, changes in size, or persistent aching should be checked by a GP.

Things people get wrong

"One testicle hanging lower means something is wrong." It's expected. Asymmetry is the norm.

"Testicle pain is always serious." Mild, brief aches can be normal (especially after arousal without ejaculation). But sudden, severe pain needs urgent medical attention — it could be testicular torsion (the testicle twisting on its cord), which is a medical emergency.

Things people ask about testicles

Why do they hurt when hit?

The testicles have a very high concentration of nerve endings and no protective bone or muscle. Even a moderate impact can cause intense pain and nausea. The pain usually passes on its own, but severe or lasting pain after an injury needs medical attention.

What is testicular torsion?

When a testicle twists on its blood supply cord, cutting off blood flow. It causes sudden, severe pain and swelling. It's a medical emergency — go to A&E immediately. If treated quickly (within a few hours), the testicle can usually be saved. [CHECK: time window for treatment]

Can the testicles go back up inside the body?

Occasionally, the cremaster muscle can pull a testicle up into the inguinal canal (near the groin), especially in cold or during arousal. This is usually harmless and temporary. If a testicle doesn't descend by puberty, a GP should assess it.

Where to get help

• Your GP — for any lumps, pain, swelling, or changes. They examine testicles regularly and won't be fazed.
• A&E — for sudden, severe testicular pain (possible torsion). Don't wait.

The testicles are two oval-shaped parts that sit inside the loose skin pouch (the scrotum) behind the penis. Most people call them balls. They have two main jobs.

The first job is making sperm — the tiny cells that can cause pregnancy. The testicles make millions of sperm every day from puberty onwards.

The second job is making testosterone — the hormone that causes many of the changes during puberty, like the voice getting deeper, body hair growing, and muscles developing.

The testicles hang outside the body because sperm need to be kept slightly cooler than body temperature to develop properly.

It's completely normal for one testicle to be a bit bigger or hang a bit lower than the other. Most people's left one sits lower.

The testicles are very sensitive. Getting hit there hurts a lot because of all the nerve endings.

It's a good idea to check your testicles every now and then for any new lumps or changes. Feel each one gently after a warm bath or shower. Testicular cancer is rare in young people but very treatable if caught early. Any new hard lump or sudden pain should be checked by a doctor.

Sudden, severe pain in a testicle is an emergency. Go to A&E straight away.