What is it?

To doctors, it is androgenetic alopecia. To lesser mortals, it is the loss of hair from the temples and crown of a man's head. (Women sometime show the classic receding hairline and bald spot after childbirth or a miscarriage, and when their testosterone levels are elevated. See below.) It is distinguished from female pattern baldness, alopecia areata, and baldness caused by extrinsic factors; all of these have different causes and effects.

The pattern

True male pattern baldness always begins with a receding hairline. From here, the hairline may recede sharply along the temples, leaving either something resembling a widow's peak or an isolated island of hair above the forehead; or else it might recede in an even line. As the case progresses, a man will also lose the hair from the top of his head (the classic bald spot); the two areas will eventually meet in the middle of the scalp, leaving only a fringe around the sides of the head. Baldness usually progresses evenly, but this varies between individuals; sometimes, the hairs will make a successful counterattack and take over previously bald areas. This is quite rare, but it does happen.

Classification: How bald am I?

Dermatologists use one of two systems to classify a case of male pattern baldness. They are the Hamilton, named after one Dr. James B. Hamilton, and the Norwood, a 1971 variant of the above. A brief summary of the Norwood system follows.

  1. Type I. No obvious hair loss.
  2. Type II. Slightly receding hairline. At this stage, baldness becomes apparent to the casual observer.
  3. Type III. Sharply receding hairline. If the hairline touches a straight line drawn across the scalp with the front edge of the ears as its endpoints, the patient has Type III baldness.
  4. Type III, vertex. Same as above, but there is a noticeable bald spot on the top of the head.
  5. Type IV. As above, but with a larger bald spot on the top of the skull. The side fringes are still connected by a band across the crown of the head.
  6. Type V. The two bald regions are still separate, but barely so. The band connecting the side fringes is narrower.
  7. Type VI. The two balding regions (hairline and top of head) meet and merge. There may be a line of sparse hair connecting the sides.
  8. Type VII. Full baldness. No hair remains on top of the head. The fringes at the side thin, and hair may be lost from above the ears and the nape of the neck.

What causes it?

First, a brief explanation of the hair growth cycle. All human hair follicles pass through three stages of life: anagen, or growth phase; catagen, or regression phase; and telogen, or dormant phase. In the anagen stage, which can last up to six years, hairs grow at an average of ten centimeters per month until they reach their maximum size and length, which is determined by the individual's genes. After this, they enter catagen, a period of two to three weeks wherein the follicle shrinks and contracts. Finally, they shift into telogen, where the hair does not grow at all. During this last phase, which lasts up to three months, the hair itself is not anchored firmly and can be pulled out with ease. The hairs that we lose while grooming all have follicles in this last stage of development.

Boooring. I wanted to know about baldness.

Normal follicles will pass through telogen and into anagen after a resting period. However, this cycle is interrupted when a man carries the genes for baldness. The culprit is a hormone known as 5α-reductase, produced in the hair follicles, which changes the male sex hormone testosterone into dihydrotestosterone (or DHT). This hormone binds to receptors on the follicles, preventing them from ever leaving telogen. Interestingly, only the follicles on top of the head are affected; DHT causes some facial and body hair to grow. Thus we have the apparent "migration" of hair from the scalp to other places.

Aha! I knew that baldness is a sign of virility.

Sorry to disprove a comforting myth, but the facts are more complex: Testosterone alone does not cause baldness. While artificially increased testosterone levels (e.g. those that result from the use of anabolic steroids) may hurry the natural progression of a pre-existing condition, and women exposed to high levels of testosterone may begin balding, merely raising androgen levels is not enough. The sufferer must have a genetic predisposition to baldness, and he must have low levels of androgen antagonists (hormones that either metabolize testosterone or block its absorption). To summarize:

  • A man with the baldness gene1, high testosterone, and many androgen antagonists will have little free testosterone in his bloodstream: He will not go bald.
  • A man with the baldness gene, low or moderate testosterone, and few androgen antagonists will have lots of free testosterone: He will go bald.
  • A man without the baldness gene will not go bald without external causes.

Who gets it?

Anyone who carries the gene(s) and has normal testosterone levels. Patterns and frequencies of the condition vary across ethnic lines; Caucasian males have, approximately, a 10% chance of going bald for each decade of life, while Chinese, African American, and American Indian men have much better odds, only a 5% chance per decade. (Note that male pattern baldness is inextricably linked to testosterone, so nobody will develop it before puberty2.) It can strike at any time thereafter; the author of this piece noticed the first signs of baldness at the age of 17. The curve levels off around the age of 80: If a man has not lost his hair by then, he will probably never lose it.

Male pattern baldness in women: WTH?

It happens, but rarely. Women can and do carry the gene for male pattern baldness, but their generally lower testosterone renders it insignificant. However, if a woman's testosterone levels rise3, the process is the same: excess testosterone is converted into dihydrotestosterone, which kills the hair follicles. Some synthetic hormones, such as those found in birth control pills, may be metabolized to testosterone and thus promote baldness, but this is rare. There is also a separate condition known as female pattern baldness, which has different causes and symptoms; hair loss is spread evenly across the head, with no discernable pattern.

Can it be treated?

Yes. Here are a few options:

Surgical treatments

  • Castration. Since baldness is directly linked to testosterone, and the testes are the primary producers of the hormone, this is the only treatment that works every single time. Few men opt for it. I can't imagine why.
  • Hair transplants. Briefly, this procedure involves transplanting healthy hair follicles to bald regions of the scalp. This can be done in large bunches (macrografts) or one hair at a time (micrografts). It is an expensive and lengthy procedure, but works every time.
  • "Flap" surgery. Here, a hairless section of the scalp is removed and the remainder of the scalp stretched to cover the resulting hole. It works, but is only a temporary fix.

Pharmaceutical treatments

  • Rogaine (topical minoxidil). Clinical trials have proven it effective in slowing the rate of hair loss for about 75% of users, and causing some hair regrowth in about 66%. It is available over the counter. The patient must use it continually or all results will be lost. Side effects include itching, rashes, and blue pillows4.
  • Propecia (finasteride). This was originally prescribed to treat enlargement of the prostate gland, but is now known to be an effective treatment for baldness. It works by blocking the production of dihydrotestosterone, and has been proven effective in about 80% of cases. Its side effects are a bit more troublesome: about .2% of users report loss of libido or absolute impotence. It can also cause birth defects if handled or swallowed by pregnant women.
  • Combination of the above. Since they work in different ways, some men have tried using both drugs. There is no clinical data on this treatment.
  • Snake oil. The FDA has not approved any other treatments, and reliable clinical data is not available. Other treatments may work, or they may do nothing but line the pockets of the unscrupulous. Try them at your own risk.
There are also various cosmetic treatments, none of which alleviate the underlying cause of the condition.

Famous bald people

Just a few off the top of my head:

/msg me if you have another to add.


1 What's a baldness gene? This is not yet fully understood. It is known that baldness is genetic, and current thought holds that it is sex-linked: A bald father will not necessarily have bald sons. To determine your chances of going bald, look at your maternal uncles. If the majority of them are bald or balding, your outlook is bad.
2Barring exposure to high levels of testosterone, or certain rare conditions like progeria.
3This might happen if she develops cancer of the adrenal glands, cancer of the ovaries, or polycystic ovary syndrome. Anabolic steroids can also raise a woman's blood testosterone levels.
4 This is not a slang term. If worn to bed, it can turn a white pillowcase blue overnight.


Sources:
http://www.aad.org/PressReleases/gene_mapping.html
http://www.aad.org/PressReleases/hairlossAware.html
http://www.aad.org/PressReleases/HairScare.html
http://www.aad.org/PressReleases/microspace.html
www.keratin.com
, for all sorts of useful information on hair and the loss thereof.

Comments and criticisms are welcome.

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