Dihydrotestosterone (DHT) is a male hormone (androgen) which is produced in the prostrate gland, testes and hair follicles. Primarily it is synthesized by the adrenal glands. It is produced when an enzyme 5-alpha-reductase reacts with the hormone testosterones (frees testosterones). Despite that fact that testosterones are regarded as male hormones, they are also found in trace amounts in women where they help in building muscle mass. Testosterones are actively involved in causing androgenic alopecia.

Action of DHT-

DHT binds with the receptor sites on the scalp and disrupt the receiving of the nutrition to the hair follicles. As a result of this, the hair follicles move quickly from the growing stage to the resting phase. In this phase, the hair tends to be thin and fragile due to which is breaks and gets uprooted easily. This phase is also known as hair atrophy in which the hair falls but does not grow again, resulting in a bald patch.  Basically DHT does not allow the hair follicles to get nourished. DHT settles in the hair follicles and prevents the proteins, vitamins and minerals from reaching the hair thus, the hair is not able to sustain itself for long. Thus, the hair grows at a slower rate.

There are two different chemical forms of the enzyme 5-alpha reductase which are called as isozymes. They are referred as

• type I
• type II

Both the enzymes serve the same functions i.e. catalysis of conversion of testosterone into DHT.

Researchers and practicing dermatologists specializing in alopecia areata are of the opinion that these DHT molecules enter and spread into the interior of the hair follicle cells such as cytoplasm or cytosol and bind to androgen receptors. Together the receiver and the DHT molecule reach the nucleus of the cells. On reaching the nuclease, they disrupt protein synthesis. This is one of the factors that trigger baldness in men who are genetically inclined to baldness.

Most of the hair loss drugs have active agents that inhibit the action of 5-alpha reductase. Propecia and Avodart are two important drugs that inhibit both the types of this enzyme. Propecia has finasteride as the active ingredient and can arrest the type II enzyme while Avodart has dutasteride and inhibits the action of type I enzyme.

Once the level of DHT is lowered in the scalp, these drugs stabilize hair loss and promote the growth of healthy hair in the crown area and have been effective in 35 % of men who use these drugs. The response also varies in different age groups. In younger men, the extent of alopecia areata is not aggravated due to which the hair loss can be controlled while in older men the hair loss is at a greater extent so the effect is a lot less.

How do the drugs control the increase in DHT?

Both the drugs increase the level of testosterones in the blood by inhibiting the action of 5-alpha reductase. Testosterones play an important role in maintaining the health of the scalp and in turn help to arrest hair fall.

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