Scrotum

The scrotum is the pouch of skin that hangs behind the penis and holds the testicles. It might not look like it's doing much, but it has an important job: keeping the testicles at the right temperature for sperm production, which is slightly below normal body temperature. That's why it hangs outside the body rather than being tucked inside.

• The scrotum is the skin sack that holds and protects the testicles.
• It regulates temperature by pulling the testicles closer to the body when cold and letting them hang lower when warm.
• It's completely normal for one side to hang lower than the other — most people's left testicle sits slightly lower.
• The skin of the scrotum is thinner and more sensitive than surrounding skin.
• During puberty, the scrotum grows, darkens in colour, and begins to develop some hair.

[DIAGRAM: Labelled diagram of male reproductive system with scrotum highlighted, showing testes inside]

What it does

Sperm are produced in the testicles, but they need to be kept at about 2-3°C below core body temperature to develop properly. The scrotum acts as a built-in temperature regulator. When it's cold, the muscles in the scrotum (the cremaster and dartos muscles) contract, pulling the testicles up closer to the body for warmth. When it's warm, they relax, letting the testicles hang lower and further from the body to cool down.

This is why the scrotum looks different at different times — tighter and more compact after a cold shower, looser and more relaxed in warm weather or after a hot bath. It's also why the testicles pull up close to the body during arousal and before ejaculation.

What it looks like

Scrotal skin is thinner and more wrinkled than the skin on the rest of the body. It often has a slightly different colour — darker than the surrounding skin, which is normal. After puberty, some hair grows on the scrotum. The skin can also have small bumps (hair follicles or sebaceous glands) which are normal and not a sign of infection.

One testicle usually hangs lower than the other — this is normal and actually practical (it stops them squashing together). For most people, the left testicle is the lower one, though it can be either.

Things people get wrong

"The scrotum is just skin." It's more than that — it contains muscles that actively regulate temperature. It's a functional part of the reproductive system, not just a container.

"One testicle hanging lower means something is wrong." It's expected. Perfectly symmetrical testicles are actually less common than slightly uneven ones.

"Tight underwear damages sperm." There's some evidence that very tight, restrictive underwear can slightly raise scrotal temperature, which could theoretically affect sperm quality over time. But for most young people, this isn't something to worry about. Wear whatever is comfortable. [CHECK: current evidence on underwear and sperm quality]

Things people ask about the scrotum

Why does my scrotum change size?

Temperature regulation. It tightens in the cold and relaxes in the heat. It also tightens during arousal. This is all normal — it's the muscles doing their job.

Is it normal for the skin to be wrinkly?

Yes. Scrotal skin is naturally thin and wrinkled. This allows it to stretch and contract as the testicles move. It's supposed to look like that.

What if I notice a lump in my scrotum?

Most lumps are harmless (like cysts or varicoceles), but any new lump in or on the scrotum should be checked by a GP. Testicular cancer is rare in teenagers but does occur — and it's very treatable when caught early. Getting into the habit of occasionally checking your testicles for changes is a good idea.

Can the scrotum get injured?

Yes — and it hurts a lot because the area is very sensitive. A direct hit to the testicles can cause sharp pain and nausea. The pain usually passes on its own, but severe or lasting pain after an injury needs medical attention.

Where to get help

• Your GP — for any lumps, pain, swelling, or changes in the scrotum or testicles.
• NHS 111 — for advice on whether a symptom needs urgent attention.

The scrotum is the loose pouch of skin that hangs behind the penis. Inside it are the two balls (testicles). Its main job is keeping the testicles at the right temperature for making sperm, which needs to be slightly cooler than the rest of the body. That's why the testicles hang outside the body instead of being inside.

The scrotum changes shape depending on temperature. When it's cold, the skin tightens and pulls the testicles closer to the body to keep them warm. When it's hot, it relaxes and lets them hang further away to cool down. This is completely normal.

It's normal for one side to hang a bit lower than the other. Most people's left one sits slightly lower. The skin is thinner and more wrinkly than the skin on the rest of the body. It often gets a bit darker in colour during puberty, and some hair grows on it.

The area is very sensitive. Getting hit there hurts a lot. The pain usually goes away on its own, but if it's really bad or lasts a long time, see a doctor.

If you ever notice a new lump in this area, get it checked by a doctor. Most lumps are harmless, but it's always worth making sure.