Hair loss during adolescence can mean a person may be sick or just not eating right. Some medications or medical treatments, like chemotherapy treatment for cancer, also cause hair loss. People can even lose their hair if they wear a hairstyle that pulls on the hair for a long time, such as braids.

When discussing baldness, which affects an estimated 40 million men and 20 million women in the United States, the topic is generally about a hereditary condition called androgenetic alopecia. Ninety-five percent of hair loss is of this variety.

Male-pattern baldness refers to the upward retreat of the hairline from the forehead, as well as an expanding area of fallout from the crown of the head. In the end, all that might be left is a horseshoe-shaped fringe around the sides and back of the head. Female-pattern baldness, which recently has received more attention since Pharmacia& Upjohn began packaging and marketing Rogaine separately for women, refers to a diffuse pattern of hair loss throughout the scalp.

Normal Hair Growth

About 90 percent of the hair is growing at any one time, and the growth phase lasts between two and six years.

Ten percent of the hair is in a resting phase that lasts two to three months, and at the end of its resting stage the hair is shed.

When a hair is shed, a new hair from the same follicle replaces it and the growing cycle starts again.

Scalp hair grows about one-half inch per month, but as people age their rate of hair growth slows.

Most hair shedding is due to the normal hair cycle, and losing 50 to 100 hairs per day is expected and is no cause for alarm.

Since the follicle is a very sensitive it does respond to imbalances in the body. Most hair loss causes by disease or illness is temporary and resolves itself after the body has returned to a healthy condition.

Hair Loss Causes

High fever, severe infection, severe flu

Sometimes one to three months after a high fever, severe infection or flu, a person may experience hair loss, this is usually temporary and corrects itself.

Thyroid disease.

Both an overactive thyroid and an underactive thyroid can cause hair loss. Thyroid disease can be diagnosed by your physician with laboratory tests. Hair loss associated with thyroid disease can be reversed with proper treatment.

Other Hair Loss Factors:

There are other factors that can also cause hair loss, including but not limited to:

·Illness

·Hormonal changes

·Pregnancy, childbirth, and birth control pill usage

·Nervous habits

·Chemotherapy

"Over time, an excess build-up [of DHT] in the follicle causes it to begin shrinking, which in turn alters the natural resting and growth phases of the hair," says Reed, clinical associate professor of dermatology at NYU Medical Center, and a specialist in female hair loss. Some of the follicles eventually die, while others are rendered incapable of producing or maintaining healthy hair growth. The end result, says Reed, is hair loss -- and a condition that is medically known as androgenic alopecia.