Somewhere between the ages of 9 and 15, your pituitary gland releases hormones that tell your body to start making testosterone. Puberty begins and brings changes. Your testes (testicles), scrotum, penis, and pubic hair all begin to grow. Testosterone levels peak in your late teens to early 20s.

The amount of testosterone in your body may drop slightly in your late 20s through your 40s, but the change is minimal.

After 40, your total levels may drop only a small amount. But your body slowly begins to make more of a protein called sex hormone binding globulin (SHBG). This sticks to the testosterone in your blood and lowers the amount your body has available to use.

As testosterone levels fall, you’ll notice other changes to your:

Pubic hair: Like the hair on the rest of your body, it will thin and may turn gray.

Penis shape: For a small number of men, it may curve with age. This can affect its length, girth, and function. The condition, called Peyronie’s disease, is caused by physical trauma — usually because the shaft gets bent during sex. As it heals, scar tissue forms along the tunica albuginea — a tough sheath around the spongy tissue that fills with blood to create an erection. The scarred portion can’t expand, causing a curved erection. The condition can often be corrected surgically or treated with medications.

Testicles: The small organs inside your scrotum mostly exist to make sperm. As your testosterone levels fall, sperm production slows and they shrink.

If you get hormone replacement therapy, your pituitary gland will stop sending signals to your testes to make testosterone, and they will shrink more.

If you’re over 40, a hydrocele can also make your scrotum sag. It happens when fluid builds up around one or both testicles. Maybe your body makes too much liquid, or perhaps it can’t drain well. It’s generally painless. If you notice swelling or feel any discomfort, see your doctor.

Penis function: The nerves in your penis get less sensitive as you age. This can lead to trouble with arousal and having an orgasm. As testosterone levels drop, erectile dysfunction becomes more likely. You may lose rigidity, but not necessarily your ability to have intercourse.

Changes in your sex organs and sexuality are a normal part of aging. Talk to your doctor if age-related changes are affecting your life and relationships. Effective treatment is available.