Teen Boys' Health

Testicles FAQ

Testicles, also called testes or balls, are oval-shaped organs that sit in a sac that hangs behind the penis.

The main job of testicles is to make and store sperm and produce testosterone. That's the male hormone that's responsible for the changes that occur during puberty. Puberty is the time in your life when your body begins to change and you start to look more and more like a grown-up.

After puberty is finished, the testicles will produce millions of sperm a day. Sperm mixes with a white, milky substance to make semen. Semen is what's released from the penis when you ejaculate.

Guys become fertile, meaning they are able to ejaculate semen and get a girl pregnant, around age 11 to 17.

When will my testicles begin to grow?

Your testicles will grow during puberty, usually in the early stage of puberty, around age 10 to 13. As your testicles grow, the skin around the scrotum -- the sac that holds the testicles -- will darken, hang down, and begin to develop hair.

How big are testicles?

On average, testicles grow to be about 2 to 3 inches in length and 1 inch in diameter.

Is it normal to have one testicle that's bigger than the other?

Yes. It is common for guys to have slightly different size testicles. Usually, the right testicle is larger than the left. Also, one testicle (usually the left) often hangs lower than the other.

Why do my testicles shrink when I get cold?

For your testicles to produce sperm, they must be kept at just the right temperature. As a result, your scrotum will change size to make sure the testicles stay at that right temperature. This happens without you even thinking about it. So, when you are cold, your body sends a message to the scrotum to shrivel  to preserve heat.

Why do my testicles hang down?

Just as your body directs your scrotum to shrivel when it is cold, your body tells the scrotum to loosen up when you are too warm. Your testicles will become larger and more floppy to release the extra heat.