MadSci Network: Medicine

Re: Does cutting hair, or shaving a beard, make it grow faster? If so, why?

Date: Mon Mar 2 14:08:09 1998
Posted By: Carolyn Pettibone, grad student, Genetics, Harvard Medical School
Area of science: Medicine
ID: 888004433.Me

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!


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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