By far the most common form of hair loss and hair thinning is determined by our genes and hormones: Also known as androgen-dependent, androgenic, or genetic hair loss. It is the largest single type of recognisable alopecia to affect both men and women. It is estimated that around 30% of Caucasian females are affected before menopause. Other commonly used names for genetic hair loss include common baldness, diffuse hair loss, male or female pattern baldness.
The rate of hair shedding in androgenic alopecia is speeded up by three forces: advancing age, an inherited tendency to bald early, and an over-abundance of the male hormone dihydrotestosterone (DHT) within the hair follicle. DHT is a highly active form of testosterone, which influences many aspects of manly behaviour, from sex drive to aggression.
The conversion from testosterone to DHT is driven by an enzyme called 5-alpha reductase, which is produced in the prostate, various adrenal glands, and the scalp. Over time, the action of DHT causes the hair follicle to degrade and shortens the anagen phase. Thought the follicle is technically still alive and connected to a good blood supply–it can successfully nurture a transplanted follicle which is immune to the effects of DHT–it will grow smaller and smaller (figure 3). Some follicles will gradually die, but most will simply shrink to the size they were when you were born which produce weaker hairs. With a steadily shorter anagen growing cycle, more hairs are shed, the hairs becoming thinner and thinner until they are too fine to survive daily wear and tear. Balding hair gradually changes from long, thick, coarse, pigmented hair into fine, unpigmented vellus sprouts.
However, the sebaceous gland attached to it remains the same size. As the hair shafts become smaller, the gland continues to pump out about the same amount of oil. So as your hair thins, you will notice that your hair becomes flatter and oilier.
But the hormonal link in balding is complex. Eunuchs, who produce no testosterone, never go bald — even if carrying a baldness gene. However, if castrated men with a family history of baldness are given testosterone, they lose hair in the classic horseshoe-shaped pattern.
Studies show that while balding men don’t have higher than average circulating testosterone levels, they do possess above-average amounts of a powerful testosterone derivative, dihydrotestosterone in the scalp follicles. In male balding, genetically primed follicles convert circulating testosterone to dihydrotestosterone, which successively diminishes or miniaturises follicle size, producing ever weaker hairs. With a steadily shorter anagen growing cycle, more hairs are shed, the hairs becoming thinner and thinner until they are too fine to survive daily wear and tear. Balding hair gradually changes from long, thick, coarse, pigmented hair into fine, depigmented vellus sprouts.
Other physiological factors might cause hair loss. Recently, a group of Japanese researcher reported a correlation between excessive sebum in the scalp and hair loss. Excessive sebum often accompanying thinning hair is attributed to an enlargement of the sebaceous gland. They believed excessive sebum causes an high level of 5-alpha reductase and pore clogging, thus malnutrition of the hair root.
Although this condition could be hereditary, they believe diet is a more prominent cause. The researchers note that Japanese hair was thick and healthy, with a small gland and little scalp oil, until the occidental habit of consuming animal fat crept into their diet after World War II. This change has led to a significant height increase in the Japanese population, but it has also resulted in more Japanese men losing hair. To some extent, their observation makes sense since problems with greasy hair have often been noted as much as six months to a year prior to when thinning hair becomes noticeable, but this might be just one of the symptoms, not underlying cause, more research is needed. Most doctors agree that if you have a oily scalp with thinning hair, frequent shampooing is advised. shampooing can reduce surface sebum, which contains high levels of testosterone and DHT that may reenter the skin and affect the hair follicle.
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