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Back in my youth (during the last century), I had heard mention of a skin condition called violin neck. I believe that in severe cases it could lead to permanent scarring. Does this, in fact, exist? If so, is it confined to aspiring professionals that practice multiple hours per day?
Without deviation from the norm, progress is not possible. —Frank Zappa
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Is this what you're referring to : https://en.wikipedia.org/wiki/.....039;s_neck ?
that is, the "mark" on the skin at the point of contact between the jaw and chinrest ?
In about 1990 I met an ex-violist who had needed surgery for "inflammation of a vestigial gill", and they showed me the scar (and how the saliva duct had re-routed itself to the left temple?!). It is exceptionally rare. I posted about it here, as I thought it was interesting, but then I deleted the post, as the person may have been identifiable, and I felt that there were other potential problems with what I had written.
The wiki article above talks of a branchial cleft cyst, which I'm sure was my friend's problem, as everything they said agreed 100% with this article's caveats about surgery (which, because incomplete, had failed to cure the problem). Ears seem to have evolved from gills, but "branchial" means "pertaining to gills", so I guess a lot of stuff in the neck is connected from the ears down. My friend had to give up professional playing, but is now a happy amateur violist, so pressure of work may have been the worst part of the problem.
The most common skin issue I can see with a violinist or violist is essentially a pressure and shear ulcer.
It's real and how much/little of playing that can cause it is heavily individualized depending on several factors.
Prevention would be to watch out for early signs and intervene early. Skin break-out, localized acne, and especially non-blanchable redness. A dark maroon spot would be even more concerning.
In addition to changing chin rest, shoulder rest, and playing form, one can apply materials and topicals to alleviate the friction and protect the skin. There are also appliances that can allow the player to hold the violin without the need for the jaw to contact the violin/viola. Men have the advantage of growing facial hair too.