About 95 percent of all cases of hair loss are the result of androgenetic alopecia (also known as male pattern baldness in men).

While some types of hair loss are easily reversible, male pattern baldness is more permanent. It occurs in a characteristic pattern on the scalp: hair loss usually begins at the temples and at the top of the head toward the back, causing a receding hairline and a bald spot. Hair loss may continue until the two sections become joined, leaving a horseshoe-shaped area of hair on the sides and back of the head. Balding may begin at any age after puberty, even in the middle teens, and can range from partial loss to complete baldness. Male pattern baldness progresses slowly and is not associated with redness, itching, or pain. Currently, there is no way to prevent male pattern baldness from occurring.

The causes of male pattern baldness are thought to be complex and are not completely understood. However, as suggested by its medical name (androgenetic alopecia), male pattern baldness seems to involve both hormonal (androgen) and genetic factors. Many different types of hormones play roles in the regulation of scalp hair, but the hormones with the largest effect are the androgens. Testosterone and its more potent derivative dihydrotestosterone (DHT) are responsible for increasing the size of hair follicles in areas such as the beard and underarm during puberty, but can also cause hair follicles in the scalp to decrease in size later in life. These contrasting responses to DHT might be explained by genetic differences in the individual hair follicles. Similarly, in men who are balding, genetically determined characteristics of hair follicles in the scalp may cause the follicles to be more likely to degrade in the presence of androgens. Hair follicles become miniaturized, and the hair consequently becomes thinner and shorter. The growing phase of the growth cycle becomes progressively shorter, which means more hairs are shed. Although the follicles still have an adequate blood supply, they continue to shrink, and some eventually die.

Female Hair Loss

The most common type of hair loss seen in women is androgenetic alopecia, also known as female pattern alopecia. Alopecia means baldness, but just as in men, it does not have to be complete hair loss. This is seen as hair thinning predominantly over the top and front of the head. It affects approximately one-third of all susceptible women.

Female pattern hair loss may begin as early as puberty. In these cases if there are signs of hormone imbalance, such as excess facial or body hair, a hormone evaluation should be done. Hormonal changes are a common cause of female hair loss.

Many women do not realize that hair loss can occur after pregnancy or following discontinuation of birth control pills. It may also follow any sudden physical or psychological stress to the body. These types of hair loss are "Telogen Effluvium" and are usually temporary. It is important to remember that this hair loss may be delayed by up to three months following the change. Up to 8 months will be required for regrowth to be fully achieved.

The most common type of hair loss seen in women is androgenetic alopecia, also known as female pattern alopecia. Alopecia means baldness, but just as in men, it does not have to be complete hair loss. This is seen as hair thinning predominantly over the top and front of the head. It affects approximately one-third of all susceptible women, but is most commonly seen after menopause

In female pattern hair loss some excess loss of hair is noted, but gradual thinning is what is what usually brings the woman to a dermatologist. Normal hair shedding is approximately 100-125 hairs per day. A lower number of hairs lost would apply to those whose hair is already thin. Hair loss occurs when the daily hair loss exceeds 100 hairs. In female pattern hair loss, when the affected hair is shed, the root grows one in its place that is shorter. Eventually it becomes invisible "peach fuzz". Genetically, hair loss can come from either parent's side of the family.

Female pattern hair loss may begin as early as puberty. In these cases if there are signs of hormone imbalance, such as excess facial or body hair, a hormone evaluation should be done. Hormonal changes are a common cause of female hair loss.

Many women do not realize that hair loss can occur after pregnancy or following discontinuation of birth control pills. It may also follow any sudden physical or psychological stress to the body. These types of hair loss are "Telogen Effluvium" and are usually temporary. It is important to remember that this hair loss may be delayed by up to three months following the change. Up to 8 months will be required for regrowth to be fully achieved.

What are some other types of hair loss?

Aside from male/female pattern baldness, some of the most common types of hair loss include:

Alopecia areata, which leads to patchy hair loss on the scalp. While the causes of alopecia areata are not completely understood, the hair loss is thought to be the result of the body's immune system attacking the hair follicle. Alopecia areata often resolves without treatment.

Traction alopecia, which results from long-term pulling on the hair. This type of hair loss can be caused by certain hairstyles, such as tight braids and hair extensions. Certain diseases, such as diabetes, systemic lupus erythematosus and disorders of the thyroid gland can also cause baldness. Sudden hair loss may be an early warning sign for some diseases and should be reported to a doctor.

Hair loss has many other causes, including illness, poor nutrition, skin damage, some medications, and certain medical treatments such as anticancer chemotherapy and radiation therapy.