Male pattern baldness is the most common type of balding among males. It affects roughly 30% of men by the age of 30, 50% by 50, and 57% by 60.
Despite years of focused research, the etiology of this condition still holds many mysteries.
One of the molecules that seems to be intimately linked with male pattern baldness is dihydrotestosterone (DHT). In this article, we will discover what DHT is, what it does and how it can be influenced.
- What is DHT?
- Hair growth and hair loss
- How DHT affects hair growth
- The role of 5-alpha-reductase
- DHT and hair loss medication
Fast facts on dihydrotestosterone
Here are some key points about dihydrotestosterone (DHT). More detail and supporting information is in the main article.
- DHT is vital for the in utero development of male genitalia.
- Testosterone is turned into DHT by enzymes.
- DHT is five times more potent than testosterone.
- More than half of men are likely to experience male pattern baldness mediated by DHT.
- DHT is an androgen and helps give males their male characteristics.
- There is no known role of DHT in female development.
- DHT causes hair follicles to miniaturize.
What is DHT?
Dihydrotestosterone's actions are responsible for male pattern balding.
The role of DHT is multifaceted and not solely hair based. It is involved in benign prostatic hyperplasia (enlarged prostate) and prostate cancer too. As such, it is a well-studied and fascinating molecule.
DHT is a sex steroid, meaning it is produced in the gonads. DHT is also an androgen hormone, from the Greek prefix "andro" meaning "masculine."
Androgens are responsible for the biological characteristics that typify males - deep voices, hairy chests and increased muscle mass, for example.
Testosterone is converted to DHT by specific enzymes. Roughly 5% of free testosterone is normally converted into DHT.
DHT is a particularly potent androgen, five times more potent than testosterone. It attaches to the same sites as testosterone but with more ease and remains bound for longer periods of time.
During fetal development, DHT plays a vital role in the development of the penis and prostate.
As an example of DHT's vital role in the development of men, this article will briefly mention congenital 5-alpha-reductase (5-AR) deficiency. The enzyme 5-AR converts testosterone into DHT. In this condition, 5-AR is missing.
Males who are born with 5-AR deficiency have severely underdeveloped prostate and external genitalia, to the extent that some are brought up as girls. Their penis may appear as an enlarged clitoris or be almost totally absent.
As an adult, DHT is the primary androgen in the prostate and hair follicles. Women have no known role for DHT during development.
Hair growth and hair loss
Male pattern baldness, also known as androgenetic alopecia, is the most common type of baldness in men. Hair at the temples and on the crown will slowly thin and eventually disappear.
There is a genetic component to male pattern baldness, and DHT is thought to be one of the major factors involved in its etiology. 2
To understand male pattern baldness, we need to understand hair growth. The following is a brief summary of normal hair growth.
Hair growth is split into three phases: anagen, catagen and telogen:
- Anagen: the growth phase. Hairs remain in this phase for 2-6 years. The longer this phase lasts, the longer the hair grows. Normally around 85% of the hairs on the head are in this phase
- Catagen: this phase lasts only 2 weeks and allows the follicle to renew itself
- Telogen: this is the resting phase where the follicle lies dormant and can last from 1-4 months. Normally 10-15% of hairs are in this phase. Once this phase is over and anagen begins again, the existing hair is pushed out of the pore by the new growth and naturally sheds.
In MPB, follicles slowly become miniaturized and the anagen phase of the hairs is reduced. Due to the shortened growing phase, the hair's maximum length is reduced. At the same time, the telogen phase lengthens. This cycle slowly becomes more and more weighted toward the telogen phase.
Over time, the anagen phase becomes so short that the new hairs do not even peek through the surface of the skin.3
Added to this, telogen hair growth is less well anchored to the scalp, explaining why there is often hair loss noted during showering.
Miniaturization of the follicles causes the shaft of the hair to become thinner and thinner with each cycle of growth. Eventually, normal (terminal) hairs are reduced to villus hairs. Villus hairs are the soft, light hairs that cover a baby and mostly disappear during puberty in response to androgens.4
On the next page, we look at the role of DHT in hair growth.