The scalp contains 100,000 to 150,000 hair follicles that continuously produce new hair. Normally, 30 to 150 hairs are shed each day, which are replaced by new hair growth. However, there are several conditions that can cause temporary or permanent hair loss.
Male pattern baldness, also known as "androgenetic alopecia," is the most common form of hair loss in men. The condition is so common that it is not considered a disease, although it can have a significant psychosocial impact on some individuals.
Women can also develop androgenetic alopecia, often with a more diffuse pattern of hair loss. However, hair loss in women is not further described in this article.
The vast majority of men experience some degree of androgenetic alopecia, but the onset, progression, and extent of hair loss can vary greatly. In 5% of cases, hair loss begins before the age of 20. Hair loss often starts at the temples ("receding hairline") and the top of the head ("bald spot"). Over time, the hairline recedes further, leading to various degrees of baldness. The diagnosis is based on information regarding family history, onset, extent, and progression of hair loss.
Androgenetic alopecia is caused by a genetically determined sensitivity to male sex hormones (androgens). In individuals with this sensitivity, increased levels of the hormone testosterone are converted into dihydrotestosterone within the hair follicles through the activity of the enzyme 5-alpha-reductase. Increased levels of dihydrotestosterone cause thehair follicles to shrink and shorten the growth phase of the hair. Eventually,the hair follicles lose the ability to produce hair, resulting in permanenthair loss.
The hair follicles located at the sides and back of the head are less sensitive to dihydrotestosterone. Therefore, hair loss in these areas is rare, leading to a horseshoe-shaped "ring" of remaining hair.
Androgenetic alopecia is a normal physiological condition and does not require treatment. However, some individuals wish to prevent or slow down hair loss due to reduced self-esteem and psychosocial burden.
There are various treatment options available, with varying degrees of effectiveness. Some treatments involve topical applications to the scalp, while others involve oral medications. It is also common to combine these approaches.
The treatments can inhibit the activity of the enzyme 5-alpha-reductase, which reduces the formation of dihydrotestosterone. This effect can slow down, and potentially reverse, some of the hair loss.
All forms of treatment must be continued without interruption to maintain effectiveness. None of the available treatments can regrow hair on a bald scalp. Therefore, treatment should be initiated early for optimal results and continued as long as one wishes to prevent further hair loss.
In cases of long-standing baldness, hair transplantation is the only treatment option. In this procedure, hair follicles from the back of the head, which are less sensitive to dihydrotestosterone, are transplanted to areas with hair loss.
There are various causes of hair loss, including disruptions in the hair growth cycles (anagen and telogen effluvium), autoimmune diseases (alopecia areata), scarring scalp conditions, infections (such as tinea capitis and syphilis), and pressure and traction injuries. However, these forms of hair loss rarely result in the classic pattern of hair loss seen in androgenetic alopecia.
