|MadSci Network: Medicine|
Hi! I love your question, because it is something I have always wondered about, but never bothered to look up before. It does seem amazing that the root of a hair could know what was happening as much as 3 feet away! And since our hair, like the surface of our skin, is technically dead, the statement that cutting or shaving hair stimulates it to grow is even more perplexing. It turns out that this is a very widespread myth, and there is absolutely no scientific evidence to back it up. I went and did some research on the subject, and found a few papers that tried to test the idea. They were pretty funny to read. The scientists conducting them had to recruit their friends to do different shaving experiments, mostly on arms, legs, or heads. They would measure the weight of hair shaved after allowing it to grow for several days, and they tried to see if more frequent shaving made the hair grow faster. But in each experiment, the scientists found that the hair didn't grow any faster no matter how often it was shaved. Hairs grow to a specific length, and then they just stop. That's why your eyebrows don't grow down over your eyelids! That's also why you might notice that a friend of yours has really long hair, and no matter how long you wait, yours won't grow any longer. The hair on each person's head, and in a man's beard, are programmed to grow for a certain amount of time and then it stops and stays there for a while before falling out. If you happen to cut it while it is in the growing phase, it will keep growing, and that might make you think that by cutting it, it was stimulated to grow. But it would have kept growing no matter what you did -- unless of course you plucked it out! I hope this answer was helpful! :)Carolyn References: Trotter M. The resistance of hair to certain supposed growth stimulants. Archives of dermatology and syphilology 1923;7:93-98. Lynfield et al. Shaving and hair growth. Journal of investigative dermatology. 1970;55:170-172.
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