Dihydrotestosterone (DHT), a derivative of the male hormone testosterone, is the enemy of hair follicles on your head. Simply put, under certain conditions DHT wants those follicles dead. This simple action is at the root of many kinds of hair loss, so we'll address it first.
Androgenetic alopecia, commonly called male or female pattern baldness, was only partially understood until the last few decades. For many years, scientists thought that androgenetic alopecia was caused by the predominance of the male sex hormone, testosterone, which women also have in trace amounts under normal conditions. While testosterone is at the core of the balding process, DHT is thought to be the main culprit.
Testosterone converts to DHT with the aid of the enzyme Type II 5-alpha reductase, which is held in a hair follicle's oil glands. Scientists now believe that it's not the amount of circulating testosterone that's the problem but the level of DHT binding to receptors in scalp follicles. DHT shrinks hair follicles, making it impossible for healthy hair to survive.
The hormonal process of testosterone converting to DHT, which then harms hair follicles, happens in both men and women. Under normal conditions, women have a minute fraction of the level of testosterone that men have, but even a lower level can cause DHT- triggered hair loss in women. And certainly when those levels rise, DHT is even more of a problem. Those levels can rise and still be within what doctors consider "normal" on a blood test, even though they are high enough to cause a problem. The levels may not rise at all and still be a problem if you have the kind of body chemistry that is overly sensitive to even its regular levels of chemicals, including hormones.
Since hormones operate in the healthiest manner when they are in a delicate balance, the androgens, as male hormones are called, do not need to be raised to trigger a problem. Their counterpart female hormones, when lowered, give an edge to these androgens, such as DHT. Such an imbalance can also cause problems, including hair loss.
Hormones are cyclical. Testosterone levels in some men drop by 10 percent each decade after thirty. Women's hormone levels decline as menopause approaches and drop sharply during menopause and beyond. The cyclic nature of both our hair and hormones is one reason hair loss can increase in the short term even when you are experiencing a long-term slowdown of hair loss (and a long-term increase in hair growth) while on a treatment that controls hair loss.
The following are the most common causes of women’s hair loss:
The majority of women with androgenic alopecia have diffuse thinning on all areas of the scalp. Men on the other hand, rarely have diffuse thinning but instead have more distinct patterns of baldness. Some women may have a combination of two pattern types. Androgenic alopecia in women is due to the action of androgens, male hormones that are typically present in only small amounts. Androgenic alopecia can be caused by a variety of factors tied to the actions of hormones, including, ovarian cysts, the taking of high androgen index birth control pills, pregnancy, and menopause. Just like in men the hormone DHT appears to be at least partially to blame for the miniaturization of hair follicles in women suffering with female pattern baldness. Heredity plays a major factor in the disease.
When your body goes through something traumatic like child birth, malnutrition, a severe infection, major surgery, or extreme stress, many of the 90 percent or so of the hair in the anagen (growing) phase or catagen (resting) phase can shift all at once into the shedding (telogen) phase. About 6 weeks to three month after the stressful event is usually when the phenomenon called telogen effluvium can begin. It is possible to lose handful of hair at time when in full-blown telogen effluvium. For most who suffer with TE complete remission is probable as long as severely stressful events can be avoided. For some women however, telogen effluvium is a mysterious chronic disorder and can persist for months or even years without any true understanding of any triggering factors or stressors.
Anagen effluvium occurs after any insult to the hair follicle that impairs its mitotic or metabolic activity. This hair loss is commonly associated with chemotherapy. Since chemotherapy targets your body’s rapidly dividing cancer cells, your body’s other rapidly dividing cells such as hair follicles in the growing (anagen) phase, are also greatly affected. Soon after chemotherapy begins approximately 90 percent or more of the hairs can fall out while still in the anagen phase.
The characteristic finding in anagen effluvium is the tapered fracture of the hair shafts. The hair shaft narrows as a result of damage to the matrix. Eventually, the shaft fractures at the site of narrowing and causes the loss of hair.
This condition is caused by localized trauma to the hair follicles from tight hairstyles that pull at hair over time. If the condition is detected early enough, the hair will regrow. Braiding, cornrows, tight ponytails, and extensions are the most common styling causes.
Reviewed by Paul J. McAndrews, MD
Hair Loss Project