Humans put a lot of time and effort into thinking of ways to hold onto their hair. Globally, the market for hair loss products is expected to reach $11.8 billion by 2024. Donald Trump’s wispy comb-over is just one example of our fascination with people’s ‘dos—or lack thereof. We all lose hair throughout our lives, but how much loss is normal?
Terminal hair, that is, the hair found on our heads, eyebrows, eyelashes, and pubic hair, is essentially three separate coils of proteins twisted tightly together and colored by melanin, a pigmenting chemical found in our skin and irises, explains Shani Francis, a dermatologist and the director of the Center of Hair Disorders in Evanston, Illinois. Whether our hair is curly or straight is mitigated by the shape of the hair follicles themselves: Symmetrical hair follicles tend to produce straight hair; asymmetrical produce curlier hair.
The growing period of head hair is anywhere between two and six years, but everyone has a combination of short and long growth period hair follicles. Anyone who grows their hair long can do so partly because more of their hair follicles have long growing periods. Most people’s hair grows at similar rates, between four and six inches per year, depending on genetics. But the length hair reaches is more related to how much wear and tear it’s subjected to, including how much it is being styled, says Francis. Pulling hair back tightly, brushing vigorously, and even drying it with a towel can break individual strands.
Hair grows in cycles, but not simultaneously. ”Each hair has its own clock,” Francis said. So, of the roughly 90,000 to 150,000 hairs on our heads, each one of them is either growing, “resting” (the hair is still in the follicle but not longer gaining length for about two to three months), or falling out, each at different rates. It’s totally normal for some strands of hair that have reached the end of their cycles to fall out on a daily basis—so don’t panic if your hair brush looks a bit like a tumble weed after a shower. Beauty blogs suggest that curly hair falls out more than straight hair after taking a shower because people with curly hair tend to brush their hair less often.
But when your hair falls out in chunks, it’s likely the sign of a synchronization problem related to some kind of major stress on the body. Pregnancy, surgery, periods of insomnia, thyroid problems, or nutritional deficiencies disrupt our hairs’ normal cycles. “The body is overwhelmed, and doesn’t want to consume unnecessary energy growing hair,” Francis says. “The body tells the hair to grow to rest prematurely.” All of a sudden, about 40% of the hair stops growing. When that resting phase is over, it falls out in large clumps. Hair can also fall out as a result of chemotherapy, but often this is because chemo attacks all rapidly growing cells, including cancer cells and hair follicles, causing immediate loss.
Gradual hair loss, especially in men, is normal with age. Hair follicles are particularly sensitive to the sex hormone dihydrotestosterone (DHT), a modified version of testosterone. When they pick up DHT, they shrink and produce smaller hairs. Although men typically produce less testosterone as they age, their hair follicle’s sensitivity to DHT increases; as a result, more of their hair follicles shrink, resulting in bald patches.
Now that we’ve evolved to wear clothing and live in climate controlled environments, for many there’s no real evolutionary advantage to having hair. But head hair still provides important functions like giving us feedback on our health, and protection from the sun. That’s something we don’t often appreciate, until it’s gone.