How long can hair grow? - Maksim Plikus

At age 44, Xie Qiuping cut her hair for the first time in over three decades. At the time, her impressive locks extended over five meters— earning the Guinness World Record for the world's longest hair. But even with this record-setting feat, her hair might not have reached its maximum possible length. So just how long can human hair actually grow? To get to the bottom of this question, let's start at the bottom of a hair follicle. Follicles are tube-shaped structures nestled roughly half a centimeter below the skin's surface. At their base is what's called the hair bulb, and it contains rapidly dividing matrix cells. As they divide, these develop into specialized hair cells called trichocytes, which harden as they fill themselves with cable-like keratin proteins. As more and more trichocytes are produced, they form a strand of hair that emerges from the follicle and grows upwards. All the hair on your body grows this way, but not all hair will grow to the same length, shape, or color. Those properties are determined by yet another type of cell within the hair bulb: the fibroblast. Fibroblasts instruct the matrix cells to grow specific kinds of hair for each part of the body. This is why doctors doing hair implants usually use follicles from the same body part, though they'll sometimes change things up. For example, eyelashes are some of the shortest hairs on your body at an average length of one centimeter. So to give people longer eyelashes, doctors might implant scalp follicles, which grow at a rate of about 15 centimeters per year. So these patients will have to trim their new lashes regularly to avoid a blinding curtain of hair. In general, our follicles are very resilient. Even if you pluck hair out with your fingers or some wax, you’ll likely only damage matrix cells, not fibroblasts. So given time, those hair bulbs will repair themselves and begin producing new hair. However, each strand of hair will only grow for so long. We don't fully understand how follicles measure time, but in most cases they'll stop growing a strand after 5 to 7 years. This means that at the rate of 15 centimeters a year, the average person’s scalp hair could reach a maximum length of around one meter. The precise duration and speed of hair growth varies from person to person depending on genetics, hormones, and various health conditions, and it’s difficult to know exactly what combination of these factors let Xie Quiping reach her record. But however long your locks may be, when a follicle stops growing, the hair falls out— shedding from our heads slowly, or in clumps during showers and hair brushing. After a hair is lost, fibroblasts will trigger the growth of a new strand to fill out your scalp— usually. As we age, follicles run out of certain cell types, which can lead to changes in hair growth. For example, when they run out of pigment-producing melanocyte stem cells, follicles begin producing gray hairs. And since there are only a handful of melanocyte stem cells per follicle to begin with, they tend to run out relatively early in a person’s life. Similarly, when follicles run out of epithelial stem cells, they begin to shrink and grow shorter, thinner strands before eventually shutting down production altogether. This is what leads to baldness, though the condition can also be accelerated by testosterone, which can prevent fibroblasts’ instructions from reaching a follicle’s cells. While it’s completely natural for hair growth to change over the course of our lives, there are ways to take more control of our scalps. Some baldness remedies remove excess testosterone, and special shampoos can address the coarse, brittle strands reported by many people with gray hair. Since our bodies already produce hair at the fastest possible biological speed, there's currently no way to grow hair faster. But even if you’re unlikely to beat Xie Qiuping’s record, with time, the right treatments, and some genetic luck, you should be able to grow some luscious locks of your own.