Experts say our tresses usually grow at the rate of about one-half inch per month -- with each hair having a growth phase of two to six years. At that point the hair "rests" for a period of time, then falls out -- and the follicle from which it sprang soon starts growing a new strand. And so the cycle continues, usually well into our senior years.
In some folks, however -- those with a genetic predisposition to hair loss -- a group of hormones called androgens interferes with this natural process. According to dermatologist Michael Reed, MD, androgen hormones include testosterone, androsteinedione, and dihydrotestosterone (DHT) -- all of which are made in men's bodies in large amounts, and in women's bodies in small amounts.
In those who are genetically susceptible, when testosterone comes in contact with enzymes residing in the hair cell, it is converted into the more potent androgen DHT, which then binds with receptors deep within the hair follicle.
"Over time, an excess build-up [of DHT] in the follicle causes it to begin shrinking, which in turn alters the natural resting and growth phases of the hair," says Reed, clinical associate professor of dermatology at NYU Medical Center, and a specialist in female hair loss. Some of the follicles eventually die, while others are rendered incapable of producing or maintaining healthy hair growth. The end result, says Reed, is hair loss -- and a condition that is medically known as androgenic alopecia.
For many decades, doctors believed that androgenic alopecia was the primary cause of balding in both men and women. Today they know this is not true -- at least where women are concerned.
Female, Male Balding Not the Same Pattern
"We don't even like to use the term 'androgenic alopecia' in women anymore -- instead we call it female pattern hair loss -- a broader term that encompasses many possible causes, some of which are likely to be directly linked to an excess of testosterone, and some of which are not," Daly tells WebMD.
Indeed, he says that although the science of female balding is still largely misunderstood, there is evidence that many other types of enzymes, as well as hormone receptors and blockers, may be at work in women.
One clue that there is a true difference between male and female balding is the pattern in which the hair loss occurs.
"Female pattern balding goes around the whole top of the head -- it's diffuse -- whereas men lose it on the temple, the crown, the bald spot in the back," says Daly. Not coincidentally, the hormone and enzyme receptor sites are also different in varying areas of the scalp -- another reason doctors now believe the loss patterns are caused by different precipitating factors.
Another important difference: While balding in men is almost always the result a genetic predisposition coupled with age, in women, it can happen at any time. In addition, underlying medical conditions can also be the cause of hair loss -- even when true androgenic alopecia is the diagnosis.
Medical Causes Common
"Often these women are also suffering with polycystic ovary syndrome, [a common hormonal problem in women], and sometimes their hair loss is the only obvious sign," says Ricardo Azziz, MD, director of the Center for Androgen-Related Disorders at the Cedars Sinai Medical Center in Los Angeles.
In addition, Daly reports that certain types of autoimmune disorders result in a slightly different and often less dramatic hair loss problem known as alopecia areata -- an inflammatory condition that causes hair to come out in clumps or patches.
Still others can develop a temporary hair shedding problem known as telogen effluvium -- a change in the natural hair growth system that often follows childbirth, crash dieting, surgery, or a traumatic emotional event.
Azizz adds that thyroid disorders, anemia, even chronic illness or the use of certain medications can also cause hair loss in women that is often undiagnosed.
For these reasons, specialists say it's vital for all women to get at the "root" of their hair loss before seeking treatment.
"The No. 1 rule of treating hair loss in women is getting the correct diagnosis -- if there is an underlying physical problem it has to be corrected first," says Reed. Often, he says, that can preclude the need for additional hair loss treatment. As such, he advises women to see a doctor who specializes in female pattern balding and make certain to be checked for possible underlying medical conditions via blood tests, or if need be, a scalp biopsy.
"Often the diagnosis is made by excluding what problem isn't there -- but it's still essential to do the complete workup," says Daly.