Mod -80, I know you’re a doc, but a poisek also? The Mishna Berurah says if you bite your nails and not use a scizzors it’s mutter. Some say this is only b’derech aaroy, not if you do this all the time. So it’s ossur to bite your nails on Shabbos if the purpose is to have short nails. S”A Simon 328 Seif 28 says if you pop a pimple to heal it -it’s ossur, but if you do it because you want to remove the stuff inside (because it bothers you), then it’s mutter. The M.B. explains a melacha sheh’ain tzricha l’gufa is only ossur md’rabbonim and with pain the Rabbonim never assured. If you bite your nails because you’re nervous and it calms you down, this would be exactly the same as a pimple. I think by most people nail biting is a form of OCD. You have the obsession and then you have the compulsion to bite.
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