Why Is It So Hard to Regrow Hair?

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Illustration: Elena Scotti

Bodies are machines designed to remind you of death, to semi-continuously blare out the fact of your mortality, warning of the end with each ache, wrinkle, and—especially—lost strand of hair. One day you have a tremendous pomaded bouncy ‘do and are destined for eternal life, the next you’re sliding down an incline toward the grave, poignantly monitoring your hairline in a little pocket mirror. So what’s hair’s deal? Why, when it starts to go, does it so rarely change its mind, to the point that only dubiously effective medications/unguents/surgeries will ever convince it otherwise? For this week’s Giz Asks, we reached out to a number of experts to find out.

William Lowry

Professor, Molecular, Cell and Developmental Biology, UCLA

Follicles go through cycles of growth, degeneration, and regeneration—whereby almost all the hairs on the top of your head are in what’s called anogen, where the hair shaft is growing out. Meanwhile, some of the follicles—maybe 5% to 10%—are in a stage called telogen, where the bottom of the follicle has degenerated and the follicle is not making new hair shaft.

When your hair falls out, that’s an indication that one of your follicles is going through this hair cycle. The timing of the resting phase can vary dramatically. When you’re young and healthy and your hair looks great, the telogen stage is short—hair follicle stem cells quickly exit their quiescent state and reactivate and regenerate the follicle, and then new hair shafts sprout up. As you get older, or less healthy or undergo various flavors of alopecia, the follicles for the most part are getting stuck in the telogen or resting phase. The stem cells there can still be activated, but they’re not getting the right signals.

There are types of alopecia that are more akin to an autoimmune syndrome, where the immune system attacks follicles and the follicles degenerate and disappear. That’s a different situation, and more rare—you can’t do much about it unless you can resolve the immune problem. But in almost all other cases of non-scarring alopecia, the follicles are still there, they’re just not getting the right signals, or maybe not getting signals at all due to hormone imbalances or stress (each follicle is connected to the nervous system, so stress is a big trigger). The longer the follicle goes without reactivating, the more that follicle shrinks, in a process called miniaturization. The follicles get smaller and smaller such that even if you were able to reactivate them, the hair shaft that would emerge would be really tiny. When people talk about their hair thinning, it’s really a combination of follicles that are not reinitiating the hair-cycle or its due to miniaturization.

In my opinion, the reason it’s difficult to regrow hair after you’ve lost it has to do with this miniaturization—the longer you go without your hair regrowing, the more the follicle itself shrinks and miniaturizes, the harder it is to get that follicle to wake back up again. And then even if you were somehow able to wake up all those follicles, those follicles might come in skinny and wimpy, so it still might appear like your follicles aren’t working, because their overall appearance would be thinner. So I suspect if you had a way to intervene to reactivate dormant hair follicle stem cells, the best thing to do would be to intervene early, before miniaturization.


Paul J. McAndrews

Clinical Professor, Dermatology, University of Southern California, who has been performing hair transplants for over 20 years

Many physicians, as well as the media, propagate the notion that hair loss is a diagnosis. But hair loss is a symptom, just like stomach pain is a symptom. So in a sense this is like asking, ‘how come stomach pain is so hard to treat?’ Well, yes, if it’s pancreatic cancer, you’re right—that type of stomach pain is very hard to treat. But if it’s coming from gastroenteritis, it should be much easier to treat.

Androgenetic alopecia—basically, female and male pattern hair loss—is an aging process. When the genetic light switch of the susceptible hair follicle turns off, that hair follicle is actually programmed to start producing a finer hair, and a finer hair, and a finer hair, until you can’t see it anymore. So a fully bald man does have hair all over his head—we just can’t see it.

Why is it so hard to treat? Well, we don’t have anything to stop the aging process. Look at tooth decay: tooth decay is an aging process. Every human being gets tooth decay, and it gets worse as you get older. A dentist doesn’t stop tooth decay; toothpaste only slows tooth decay. As someone who specializes in hair transplants, I don’t stop androgenetic alopecia. I’m like a dentist—I just fill in the cavity.

The #1 treatment for male pattern baldness is Propecia—finasteride—and I actually think of it like toothpaste. Should you start brushing your teeth when half of them are already gone? No: the sooner you get on it the better. I’m in my mid-50s, and I have a full head of hair. I’ve been on Propecia for 15 years. People say to me: you have a full head of hair, you don’t need to be on Propecia! And I say: I also have a lot of teeth, should I stop brushing? I have a financial incentive to keep my patients off Propecia, but I recommend it to everyone—I’d think it was unethical to do otherwise. I’m going to be on it for the rest of my life, and I absolutely think it’s one of the safest drugs on the market. I don’t believe any of these complaints about “post-finasteride syndrome.” None of the studies bear it out.

Minoxidil, aka Rogaine, is the other major treatment—its topical formulation will make any kind of hair thicker (including beard hair). Minoxidil and finasteride, together, are synergistic—that’s the full-court press. That said, no drugs are perfect, just like no toothpaste is perfect, because you’re treating an aging process.


Shana Marmon

Assistant Clinical Professor and Director of Clinical Research, Dermatology, New York Medical College

Hair follicle biology is extraordinarily complex. These unique mini organs are comprised of specialized structures and stem cells that interact with hormones and other molecular signals to regulate hair growth. Genetics plays a critical role in this process. So, the ability of hair to regrow can vary significantly from person to person.

In genetically predisposed individuals, normal aging, hormonal changes, inflammation, or aggressive hair styling practices can result in the constriction, miniaturization or scarring of hair follicles. A well-studied example of this is male pattern baldness. In susceptible men, androgens (male sex hormones) induce the progressive contraction of certain hair follicles resulting in a distinct pattern of central and frontal thinning.

Although there are a few therapeutics with the ability to slow hair loss in this condition, nothing has been proven to repair a follicle to regrow hair once it has been sufficiently shrunken or damaged.

Humans are born with a finite number of follicles and are unable to generate new ones. Anything that severely injures or destroys an existing follicle will likely result in irreversible hair loss.


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