Hair loss affects tens of millions of people, but not all hair loss is the same. Bottom Line Health interviewed internationally renowned hair-disorder expert Dr. Antonella Tosti about some of the more common culprits behind thinning and shedding strands.

What is considered normal when it comes to hair loss?

It’s quite normal to lose 50 to 70 hairs a day as part of the hair’s natural growth cycle, which involves alternating periods of activity and rest. The hairs that fall out already have new hairs growing in to replace them. But when a person starts shedding more than100 hairs a day, that is abnormal and suggests you may be experiencing some form of active hair loss.

It’s difficult to keep track, but one method involves washing your hair in a sinkideally one in a color that contrasts with your hair colorand counting how many hairs you see. Daily hair washers who count about 30 to 40 hairs are in good shape. (Note: If you have curly hair, don’t tend to comb or brush daily, and shampoo only once a week, you may see 200 strands or more. This is normal.)

You can also perform what dermatologists call a pull test: Grasp small sections of hair, about 40 to 50 strands, in various locations on your scalp and give a gentle tug. If more than five hairs come out in a section, you are likely experiencing active hair loss.

How typical is age-related hair loss, and what does it look like?

It’s extremely common to notice hair loss or hair thinning as one moves through their 50s, 60s, and 70s. Called androgenetic alopecia, it’s the most common hair disorder, affecting about 80 percent of men (male-pattern baldness) and 50 percent of women (female-pattern baldness). In male-pattern baldness, the hairline starts to take on an M shape, as hair recedes at the temples. Women tend to show widening of the central parting, often more accentuated at the hairline which, if viewed from overhead, resembles a Christmas tree.

With androgenetic alopecia, the concern isn’t so much that too many hairs are falling out, but rather that the hairs that replace the ones falling out are thinner and thinner. Imagine what your front lawn would look like if most of the blades of grass started losing 50 percent of their thickness. You’d start to see more and more of the earth peeking through.

Is that what’s happening with the COVID patients who are losing hair after recovering from their infection?

No, that’s telogen effluvium (TE), a condition in which multiple hair follicles enter their “rest phase” simultaneously, rather than entering it at different times as they normally would. TE is fairly common and tends to occur approximately three months after a stressful event. That can include anything from a divorce to a big move to an illness. We first saw widespread TE during the 1918 Spanish influenza pandemic, and now it’s happening again with COVID. Hair falls out quickly—you’ll notice it on your pillowcase, on your clothes, in the shower—as soon as a few weeks post-infection, and it affects up to half of all of the strands on your head. TE is easy to recognize because the hairs have a tiny white bulb at the root that you can see with the naked eye. TE due to COVID often appears four to six weeks after the infection and it’s often accompanied by scalp pain.

Does hair lost due to TE grow back?

Yes, the shedding stops in a few months and hair begins to regrow, but it can be distressing, nonetheless. If you already had androgenetic alopecia before developing TE, the new hair will grow back thinner than before.

Sometimes, though, TE can be become chronic. This tends to happen more often in women than men and may be linked with chronic stress. The main symptom is a loss of volume in the hair, mainly at the tips. Patients often report their ponytail feels smaller (with scalp peek-a-boo possible), and they end up progressively cutting their hair shorter and shorter to avoid it looking so thin at the ends.

People going through chemotherapy often lose their hair. Is that the only way cancer treatment can impact hair?

Patients taking the common breast cancer drugs tamoxifen (Soltamox), anastrozole (Arimidex), and letrozole (Femara) can develop a condition called endocrine alopecia. It usually starts about a year after treatment begins and the hair shafts become smaller and smaller, leading to all-over thinning. This is different from chemo-­induced hair loss, which happens almost immediately and involves abrupt hair loss. These breast cancer drugs, known as SERMs and aromatase inhibitors, work by blocking estrogen, and hair needs estrogen to thrive. Patients take these drugs for five years or longer, so the hair thinning continues.

Thyroid conditions are often linked with hair thinning too, correct?

Absolutely. Your thyroid regulates so many bodily functions, and when it slows down, everything slows down, including hair growth. If you suspect your thinning hair is related to hypothyroidism, ask your doctor to test your thyroid functioning. It’s a simple blood test. But if you’re taking biotin, a popular hair-loss supplement, stop taking it at least 48 hours before the blood draw, as it can skew test results. (As a side note, there’s not enough evidence to suggest biotin even helps hair growth.)

We’ve heard a lot about frontal fibrosing alopecia in the news lately. What is it?

This is a form of hair loss we’ve been seeing more often over the last several years. It usually affects postmenopausal women, causing their entire hairline to slowly recede, almost as if someone had traced a marker along the hairline, shifted the entire thing back a few centimeters or even inches, and all of the hair in between fell out. Patients may also lose some or all of their eyebrows. We don’t know why it happens, and it’s irreversible. It may be triggered by the environment. Cosmetics, including sunscreen, ingredients are possible culprits.

Are any types of hair loss reversible?

Some, like TE, reverse naturally. Others, like androgenetic alopecia, can be slowed and, in some cases, new hair growth can occur. There are currently two FDA-approved drugs for male-­pattern hair loss and one for female. For male-pattern hair loss, there’s oral finasteride (Propecia) and topical minoxidil (Rogaine). For female-pattern hair loss, topical minoxidil is approved. But many patients use different treatments off-label with their doctor’s guidance, including oral minoxidil (both genders), oral finasteride (for postmenopausal women), and more. Chronic TE may respond to oral minoxidil but not topical minoxidil. There are also treatments such as topical steroids, platelet-rich plasma (PRP) injections, and hair transplants that can restore hair, and confidence, for some patients.

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