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A friend told me that when you're sick, your hair grows faster. When I started asking a lot of questions, my friend said it's a known fact but she doesn't remember where she heard it first or what was the scientific reasoning.

Online research did not lead to any credible scientific answers that prove or debunk this. Though, it does look like that a lot of people believe in it, not just my friend.

I couldn't think of any physiological reasons for this to be true. So is it just a myth?

References:

Does facial hair grow faster when you're sick?
Does being sick make your hair grow faster?
Apparently nails and hair grow faster when you're sick. Right? Expert opinion?
Does being sick effect the growth of your hair and nails ?
Does hair grow faster when you're sick?

the-lights
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    Note that 'hair growing after death' has been debunked - the skin dries out/retracts so that e.g. beard hair stands out more. This may be the same effect. –  Oct 27 '16 at 09:58
  • @JanDoggen: [Obligatory plug](http://skeptics.stackexchange.com/questions/31446/do-nails-and-hair-continue-to-grow-after-death) – Oddthinking Oct 27 '16 at 13:05
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    I found nothing about this claim when searching with German terms. It is difficult to prove its non-existence, it's basically up to your friend to _prove_ it. You could tell her that it is known that hair grows slower when you are sick, and then wait how she reacts. – daraos Oct 28 '16 at 11:05
  • I've never heard that claim. I may have heard that hair grows thinner during illness but don't know if that's true. I do know that fingernails grow more slowly during illness to save resources. Just based on that I'd guess hair either grows the same or more slowly. – A L Oct 28 '16 at 22:00
  • Hair growth rates increase with temperature; fever raises the body temperature. It's a physiologically plausible link, but I can find no research that would prove it. – Jack Aidley Mar 25 '19 at 14:56
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    @JackAidley Could you please provide a link to the "hair growth rates increase with temperature"-claim? I find it quite interesting, bit w haven't heard this before... – Arsak Mar 25 '19 at 19:12
  • "Sick" covers a huge variety of diseases, that have not many symptoms and effects in common. Even temperature does not necessarily rise. So what exactly is meant by "sick"? – hdhondt Apr 21 '20 at 09:47

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This is not a very authoritative answer but skimming through this book on The Biology of Hair Growth leads me to doubt it. It talks a lot about the limited factors which can stimulate hair growth but there is no indication that any of this could be related to common illness. To the contrary, it mentions that severe fevers can cause hair loss.

Brian Z
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