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Some information on Dihydrotestosterone (DHT)

Male pattern hair loss, or androgenetic alopecia, is the most common type of hair loss among men.

Hormonal factors seem to play a significant role, and especially a male sex hormone known as dihydrotestosterone (DHT).

Hair loss affects around half of all men over the age of 50 years of age with a good deal experiencing it at a younger age.

DHT has also been linked to hair loss in women, but this is quite rare so we will concentrate on male pattern baldness.

Some facts on dihydrotestosterone

Here are some specific points about dihydrotestosterone (DHT).

  • Treatments that block dihydrotestosterone may help prevent hair loss.
  • By the age of 50 years, over half of the male population will probably experience hair loss mediated by dihydrotestosterone.
  • Dihydrotestosterone is an androgen and helps give males their male physical characteristics.
  • Dihydrotestosterone is thought to cause hair follicles to miniaturize, and this contributes to male pattern hair loss.

What is dihydrotestosterone?

Dihydrotestosterone has quite a few roles to play. Apart from hair production, it is linked to benign prostatic hyperplasia, or an enlarged prostate, as well as prostate cancer too.

Dihydrotestosterone is in fact a sex steroid, meaning it is produced in the testicles. It is also an androgen hormone.

Androgens are responsible for the biological characteristics of males, including the deeper voice, body hair, and increased muscle mass. During development in the womb, dihydrotestosterone plays a vital role in the development of the penis and prostate gland.

In men, the enzyme 5-alpha-reductase (5-AR) converts testosterone into dihydrotestosterone in the testes and the prostate. Up to ten percent of testosterone is normally converted into dihydrotestosterone.

Dihydrotestosterone is more powerful than testosterone. It attaches to the same sites as testosterone, but more easily. Once there, it remains bound for longer.

Hair growth and hair loss

Male pattern hair loss is the most common type of hair loss in men around the globe. Hair at the temples and on the crown slowly thin and will eventually disappear.

The actual reason why this happens is unclear, but genetic, hormonal, and environmental factors are all thought to play a role. Dihydrotestosterone is believed to be a major factor though. It has even been suggested by some trichologists that protracted wearing of hats can cut the blood supply to the scalp, resulting in hair loss

Three phases of hair growth

To understand male pattern hair loss, we need to understand hair growth.

Hair growth is split into three phases: anagen, catagen, and telogen:

Anagen is the growth phase of hair. Hairs remain in this phase for 2 to 6 years. The longer it lasts, the longer the hair grows. Normally, around 80 to 85 percent percent of the hairs on the head are in this phase.

Catagen lasts only 2 weeks. It allows the hair follicle to renew itself.

Telogen is the resting phase. The follicle lies dormant for 1 to 4 months. Normally between 12 and 20 percent of hairs are in this particular phase.

After this, anagen begins again. The existing hair is pushed out of the pore by the new growth and naturally sheds. Clearly this is still hair loss, but is negated by a new follicle replacing the last.

Hair loss

Male pattern hair loss happens when the follicles slowly become miniaturized, the anagen phase is reduced, and the telogen phase becomes much longer.

The shortened growing phase means the hair cannot grow as long as before.

Over a period of time, the anagen phase becomes so short that the new hairs do not even show through the surface of the skin. Telogen hair growth is less anchored to the scalp, making it so much easier to fall out.

As the follicles become smaller, the shaft of the hair becomes thinner with each cycle of growth. Eventually, hairs are reduced to vellus hairs, the type of soft, light hairs that cover an infant and mostly disappear during puberty in response to androgens.

Users of anabolic steroid drugs, such as athletes and body builders, have higher levels of dihydrotestosterone. These people often experience hair loss too though.

Effects

The hair on the head grows without the presence of dihydrotestosterone, but armpit hair, pubic hair, and beard hair cannot grow without androgens.

Individuals who have been castrated or who have 5-AR deficiency do not experience male pattern baldness, but they will also have very little hair elsewhere on the body.

For reasons that are not readily known or understood, dihydrotestosterone is essential for most hair growth, but it is detrimental to head hair growth.

Dihydrotestosterone is thought to attach to androgen receptors on hair follicles. Through an unknown mechanism, it then appears to trigger the receptors to begin miniaturising.

Research has found that both plucked follicles and skin from a balding scalp contain higher levels of androgen receptors than those from a non balding scalp.

Some scientists believe that some people have a genetically transmitted susceptibility to otherwise normal levels of circulating androgens, particularly dihydrotestosterone. This combination of hormonal and genetic factors could explain why some people are more likely than others to lose their hair.

Why does dihydrotestosterone affect people in different ways?

Dihydrotestosterone affects people in varying ways. This may be due to:

  • More dihydrotestosterone being produced elsewhere in the body and arriving through circulation in the blood.
  • A greater local dihydrotestosterone production in the body.
  • More circulating testosterone that acts as a precursor for dihydrotestosterone.
  • A higher androgen receptor sensitivity.
  • An increase in dihydrotestosterone receptors at the follicle site.

It is known that dihydrotestosterone binds to follicle receptors five times more than testosterone, but the amount of dihydrotestosterone in the scalp is minute compared with the levels in the prostate.

How levels of dihydrotestosterone are controlled and why they change are not yet understood by scientists.

5-alpha-reductase

5-alpha-reductase (5-AR) is the enzyme that converts testosterone into the far more potent androgen, dihydrotestosterone.

If 5-AR levels increase, more testosterone will be converted into dihydrotestosterone, and greater hair loss will be the end result.

There are two versions of 5-AR: type 1 and 2 enzymes.

Type 1 is mostly found in sebaceous glands that produce the skins natural lubricant, sebum.
Type 2 mostly sits within the genito urinary tract and hair follicles.

Type 2 is considered more important in the process of hair loss.

Medication

Male pattern hair loss can have a really negative effect on the self esteem of a man and badly impact his confidence. To help address this, some treatments have already been developed.

Finasteride, or Propecia, was approved for safety and efficacy in 1997, by the United States Food and Drug Administration (FDA), it is now used around the globe.

It is a selective inhibitor of type 2 5-AR. It is thought to act on the 5-AR enzyme that concentrates in the hair follicles to inhibit production of dihydrotestosterone.

Studies of its efficacy have given rather impressive results, but some people still have doubts as to how effective it is.

Research has shown that it can stop baldness from progressing, and that, in some cases, hair will start appearing again. However, the number of hairs that were successfully grown in a square inch of the scalp over 5 years was 227, while the average number of hairs in a square inch is roughly 2,200.

Finasteride can be taken orally, at a dose of 1 milligram every day. Injections are also possible. If treatment stops, hair loss will continue to occur.

Adverse effects have been shown to include a loss of sexual drive or desire, a reduced ability to develop and maintain an erection, erectile dysfunction, and a decrease in ejaculate. Other medication can combat these issues though.

Other causes of hair loss

Another theory proposed to explain male pattern hair loss is that, with age, the follicles themselves come under increasing pressure from the scalp.

In younger people, the follicles are buffered by the surrounding fat tissue under the skin. Youthful skin is also better at staying hydrated. As the skin becomes dehydrated, the scalp compresses the follicles, causing them to become smaller.

Testosterone also contributes to a reduction in the fat tissue, so higher levels of testosterone may further reduce the scalps ability to buffer the hair follicles.

As follicles try to maintain their status, suggest some scientists, additional enzyme activity occurs in the site. More testosterone is converted to dihydrotestosterone, leads to further erosion and more hair loss.

Further investigation of dihydrotestosterone and male pattern hair loss will hopefully enable scientists to find the cure for male pattern baldness, or at least understand the definite causes and therefore a suitable and reliable treatment.


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Further Information

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