The Scientist: Rolanda Johnson Wilkerson, Ph.D., a hair and skin researcher at Procter & Gamble.
The Answer: The life cycle of a single strand of hair is threefold: growing, resting, shedding. The anagen, or growth phase, is when your hair, well, grows. This lasts between two and six years, and when it’s done, that’s as long as the hair is going to get.
In the catagen, or transitional phase, which lasts a few weeks, that growth slows down as the hair shaft starts to lift out of the follicle. Finally, in the telogen phase, the hair is pushed out by a new hair sprouting underneath it. Your individual hairs are all at different points in this cycle, which is why you don’t periodically go bald as new shafts push out the old! Every day, about 100 get shed out and replaced by new strands.
People’s hair grows at different rates, yielding more or fewer inches in the same amount of time. And one woman’s anagen phase might last three times as long as another’s, based on genetics. That math determines your ultimate hair-growth potential. Typically, the maximum length our hair will grow is three feet, but some people’s won’t ever reach that. (On the other end of the spectrum, there’s a rare genetic condition that allows people to grow their hair to the floor!)
The hair cycle is driven by hormonal fluctuations, so it may change as you enter different life stages. During pregnancy, high estrogen levels prolong the anagen stage, so hair is likely to grow both thicker and longer. Conversely, during and after menopause, your estrogen levels drop. This can mean both slower growth and therefore shorter hair. In many cases, when a hair's shed after the telogen phase, finer hairs will replace them, causing overall thinning.
Most of this is beyond our control, but the way we care for our hair, our scalps, and our bodies is not—and can have a huge impact on the length and health of our hair. Chemical treatments, heating and sun exposure can cause your hair to break before it’s reached its full potential. It’s important to make sure you’re hydrated and to eat foods with vitamins A and C—which fuel sebum production, keeping hair supple—and omega 3 fatty acids, which boost scalp health. Hair is made up of protein, so make sure you’re eating enough of that, too.
If you care for your body and hair, it can grow. Even if your personal max isn’t as long as you wish (or as long as it used to be) good habits will keep your locks in tip-top condition.
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