If you think hair loss occurs only in men, think again. An estimated two-thirds of American women will face hair loss at some point in their lives – contributing to feelings of low self-esteem and confidence.

To understand why women lose their hair, it’s important to understand how hair grows. Generally, scalp hair grows about a half-inch per month, with each hair in a growth (or anogen) phase for two to six years. The hair then rests for one or two weeks (the catagen phase), and falls out in its telogen phase (we normally lose 50 to 100 hairs a day as part of this process). Soon, a new hair grows from the same follicle, a cycle that continues for most of our lives. At any time, about 85 percent of hair is in the growth phase.

This cycle, however, can be interrupted by hormones called androgens, which include testosterone and dihydrotestosterone (DHT). Even though these are “male” hormones, women’s bodies produce them in small amounts. When testosterone meets up with certain enzymes in the hair cells of someone with a genetic predisposition to hair loss, it converts to DHT, which causes hair follicles to shrink and die. The result is a type of hair loss called female-pattern baldness. The medical term is androgenetic alopecia.

Androgenetic alopecia in women also can be linked to other hormone-related conditions including polycystic ovary syndrome, pregnancy, menopause, and taking certain birth-control pills.

This hereditary female-pattern baldness differs from the male version in one major way. In women, the hair loss is much more diffuse – it tends to thin all over the scalp, while a man’s hairline recedes and the crown thins, leaving a U-shaped ring of hair around the sides and back of the scalp. But it’s no less distressing for a woman, and affects an estimated 30 million American women – making it the most common cause of female hair loss.

Telogen effluvium is the second-most common type of hair loss I see in my practice. When a woman’s body goes through a traumatic experience – such as childbirth, major surgery, an emotional shock or severe stress – it can cause the 85 percent of hair that’s in the growth phase to shift all at once into the shedding phase. Crash dieting, with too little protein or iron, can also cause telogen effluvium. Once the stressful situation resolves – or nutrition improves – the hair loss usually does, too.

Thyroid disorders are another potential cause of hair loss – and women are five to eight times more likely than men to have thyroid disease. Hashimoto’s thyroiditis and Graves’ disease are two forms of autoimmune thyroid disorders in which hair loss is often seen.

There also is an autoimmune skin disease called alopecia areata that causes hair loss. It usually starts with small, round and smooth patches on the scalp and can progress to other parts of the body.

In addition, certain medications can contribute to hair loss. These include oral corticosteroids (like prednisone), and some antacids, blood thinners, NSAIDs, beta blockers and antidepressants.

Finally, the way you treat your hair can affect whether it stays on your head. Traction alopecia is a condition often experienced by women who wear tight braids or constantly pull their hair back in tight ponytails, damaging the hair follicle and preventing new hair growth in certain areas of the scalp. Trichotillomania – hair loss caused by compulsive twisting or pulling of the hair until it breaks off – affects as many as 10 million Americans, most of them women. And over-processing with chemical dyes, bleaching, perms and straightening processes can cause the hair shaft to break. When the harsh treatment has stopped, however, the hair usually grows back.

With so many potential culprits, it can take some detective work to get to the root of what’s causing a woman to lose her hair. And it’s not uncommon for there to be more than one reason for her hair loss. Dermatologists have specialized expertise in diagnosing and treating conditions that affect the skin, nails and hair, so we’re best able to diagnose the underlying cause – or causes – of hair loss. And an accurate diagnosis and timely treatment offer the best chance for successful, healthy regrowth. For female-pattern baldness, in particular, having a full and healthy head of hair again can be a reality with today’s advances in hair transplantation and restoration.

Timothy Jochen, MD, is a board-certified dermatologist with special expertise in hair transplantation and restoration surgery and an associate clinical professor of dermatology at the University of Southern California. He is a member of the International Society of Hair Restoration (ISHRS). To learn more, visit www.contourderm.com.