Presented by: Anthony Oro, MD, PhD
Professor of Dermatology
January 19, 2017
Think of a head of hair as a matter of seed and soil. Hair follicles are seeds, and the soil is your scalp and body.
Every seed comes with a “warranty,” or lifespan. Once gone, it’s replaced by a new seed that takes root when the soil is healthy. That’s the picture presented by Anthony Oro, MD, PhD, at a lecture on hair loss at the Stanford Health Library.
“Every hair on your head—all thousands of them—come from stem cells,” said Dr. Oro, professor of dermatology at Stanford University School of Medicine. These hair-follicle stem cells hold the genetic encoding instructions that decide a hair’s color, texture, and size.
The hair-follicle stem cells (the seeds) flourish or not depending on whether their environment in the scalp and body (the soil) is healthy. So, in a sense, the hair cells act like “biosensors of the body” reflecting overall health, Dr. Oro said.
The genes encoded in hair cells can produce wildly different kinds of hair, as seen in different animals. Mice grow hair that is similar to humans, but only up to about 1.5 inches long, Dr. Oro said. One breed of rabbit has a mutation known as angora. “They look like a big ball of fur, because their hair doesn’t stop growing,” Dr. Oro said.
The hair on sheep shows patterns that are genetically encoded. Some sheep have specific proteins that makes their hair curly, which makes room for lots of air and space. That produces merino wool, prized for its softness and light weight. Other sheep, called Dorpors, have proteins for a hybrid wool that’s straight and dense, making especially warm sweaters.
In humans, each person has different kinds of hair stem cells on different parts of their body. On the scalp, hair cells are coded to produce the equivalent of Redwood trees—thick, strong, tall or long shafts that can reach down to the waist, Dr. Oro said. But on arms, the hair cells are coded to produce hair that’s much thinner and shorter.
Eventually, even the long hair on your head stops growing. That’s because there is a genetically encoded growth cycle for each hair that lasts 2 to 4 years. The hair stem cells live for about 40 cycles, or growth seasons, until they fall into a resting state. So hair growth continues for 40 cycles of 2-4 years each—in some cases lasting all or most of a person’s life.
The hairs don’t all stop growing or get replaced at the same time, however. The cycles all start at different times, so when one is winding down, another is ramping up. Each person loses about 100 hairs a day, on average, Dr. Oro said. And they’re replaced by 100 new hairs each day.
How long and robustly hair grows depends not only on the hair stem cells, but also on their environment. “Different parts of the body have different kinds of ‘soil,’ ” Dr. Oro said.
Factors that make the hair-cell environment healthy—or not—include nutrition, hormones, stress, inflammation, and medicines, Dr. Oro said. A robust body of research shows certain nutrients affect hair growth. Iron, zinc, and biotin are good. Heavy metals (found in some drinking water) are bad.
People don’t need to take nutritional supplements to get enough iron or zinc if they eat healthy meals, Dr. Oro said. “What you need is enough. More is not better,” he said.
Hormones can increase someone’s susceptibility to baldness, even in youth. Male pattern baldness can start in a man’s teens, 20s, 30s, or 40s and is linked to sensitivity to the male hormone DHT (dihydrotesterone). In women, lower levels of estrogen are linked to female pattern baldness.
Stress can also affect hair growth, Dr. Oro said. Studies have found nerve fibers can wrap right around hair-follicle stem cells. The nerves can produce chemicals called peptides that affect the hair cells. When stressed, some people shed hair.
Certain medicines are also known to reduce the rate of hair growth, Dr. Oro said. They include some antidepressants, blood pressure medicines, blood thinners and antigout medicines. Doctors at the Stanford Hair Clinic in Redwood City can work with patients to see if any of their medicines are causing this problem, Dr. Oro said.
Although hair loss is a normal part of aging, some people start to show baldness even when they are young adults, Dr. Oro said. Hair loss in younger people usually shows a particular pattern on the scalp called “male pattern baldness” or “female pattern baldness.”
Pattern baldness is similar to the baldness from aging in that hair shafts get smaller and growth cycles gets shorter. As a person ages, the outer covering on the hair shaft thins. Replacing it with conditioner, and protecting it from damaging sunlight or harsh chemicals, becomes important.
But there are differences. Pattern baldness affects distinct areas on the scalp, but not all areas. (In men, it typically starts at the temples and moves back; in women, it often starts at the top of the crown and spreads out.) In contrast, baldness from normal aging is more evenly distributed all over your scalp.
Pattern baldness can occur from reduced blood flow to hair follicles, or because a person is sensitive to hormones that accelerate hair loss. The male hormone DHT is a culprit, and so is the female hormone estrogen. Pattern baldness is also affected by high stress and inflammation in the body.
Male pattern baldness often isn’t a simple question of heredity. “It doesn’t necessarily come directly from your mother or father,” Dr. Oro said. Dr. Oro said, “It’s really complicated genetics.”
Baldness from normal aging isn’t so much from sensitivity to hormones or stress as a matter of the hair “seeds” (stem cells) reaching the end of the normal “warranty” (lifespan), Dr. Oro said. He added, “It’s really clear that stress and inflammation make the aging process more rapid.”
When a person feels highly stressed, they can get small patches where hair falls out that are temporary, Dr. Oro said. When the stress eases, new hair can grow in and the patches disappear.
Treatments vary depending on the causes of hair loss, Dr. Oro said. For male pattern baldness, common prescriptions include finasteride (Propecia) and dutasteride (Avodart). For female pattern baldness, estrogen replacement or topical estrogen can be used. Other treatments sometimes used to improve blood flow to the hair follicles are minoxidil (Rogaine) and the HairMax LaserComb, Dr. Oro said.
Products called “hair helmets” shine a red light on the scalp at night to stimulate blood flow and can cost up to $2,000, Dr. Oro said. The FDA has approved these products and they are safe, but Dr. Oro said there’s no proof yet that they work in most people.
Hair transplants have been available to treat baldness for quite a while, and they can improve baldness substantially, Dr. Oro said. One type, autologous follicular-unit transfer, replaces old worn-out hair stem cells with younger hair-stem cells from the person’s own scalp. “It works,” Dr. Oro said.
For a less common type of hair loss called alopecia areata, there is one very effective treatment available, Dr. Oro said. The condition is caused when the immune system mistakenly attacks hair follicles. It can affect eyebrows, eyelashes, and every hair on a person’s body.
Tofacitinib, a drug previously used for rheumatic disease, can produce a dramatic improvement in alopecia areata. “People who were completely bald for 20 years now have a full head of hair,” Dr. Oro said, describing how well the drug works. Tofacitinib is a JAK inhibitor on the market for rheumatoid arthritis, but it is not yet approved for hair loss. The Stanford group continues to perform trials on JAK inhibitors for autoimmune hair disorders.
Hair loss isn’t the only indignity that aging inflicts on hair. Going gray is another bane. But some people gray faster than others. Dr. Oro cited a rule of “50-50-50” to estimate the odds of going gray: 50 percent of hair turns gray in 50 percent of people by age 50.
Graying occurs when melanocytes, the cells that produce pigment injected into hair shafts, grow weak or die. While genetics are probably a factor in why some people go gray sooner than others, melanocytes can also be damaged by sun exposure, high stress and harsh chemicals, Dr. Oro said.
Sun protection (by wearing hats) can prevent premature aging of the hair melanocytes, Dr. Oro said. Hair coloring itself doesn’t necessarily increase grayness, but it’s a good idea to avoid harsh chemicals like peroxide. Using hair conditions to protect the outer covering of the hair shaft helps. So can reducing stress.
One type of treatment called platelet-rich-plasma, or PRP, is also sometimes advertised as a hair-loss remedy, Dr. Oro said. PRP is commonly used to help heal sports injuries. When it’s used for hair-loss treatment, blood cells called platelets are extracted from the person and injected back into the scalp. So far, the data on how well it works for hair loss, and whether it is worth the money, is “sketchy,” Dr. Oro said.
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