What happens in hair loss depends on its cause.

Inherited hair loss

Inherited hair loss (androgenetic alopecia) often begins between the ages of 12 and 40, and about half the population has some hair loss by about 50 years of age.1, 2 The hair loss generally is gradual. Men tend to lose hair on the front hairline and forehead and on top of the head. Eventually, only hair around the ears, the sides, and back of the head remains. Women with this condition typically have gradual hair thinning throughout the scalp. This type of hair loss must be treated early for hair to regrow.

See an illustration of typical inherited hair loss.
Other causes of hair loss

Alopecia areata is hair loss caused when the immune system attacks hair follicles, where hair growth begins. It usually starts with one or more small, round, smooth bald patches on the scalp and can progress to total scalp hair loss or complete body hair loss. It often begins in childhood. The hair usually grows back within 1 year. However, hair loss in alopecia areata often comes and goes—the hair will grow back over several months in one area but will fall out in another area.

Hair loss may be caused by stress, disease, or medications or medical treatments. In these cases, clumps of hair may fall out. However, after the underlying cause is stopped, the hair usually grows back, although sometimes treatment may be needed.

Treatment to regrow hair does not work for everyone. If your hair loss is inherited, treatment may not permanently restore your hair. If your hair loss is caused by medication, stress, or damage, hair often grows back after the cause is removed, although sometimes you will need treatment.

For both men and women, hair thinning and baldness increase the risk of sunburn and skin cancer on the scalp. When in the sun, it is important to wear a hat or use a sunscreen with an SPF of 30 or more to prevent sun damage to the scalp.