For years my sister has been pinching her upper arm to the point where it'll leave zit-like marks (I think she pops pores or something?). I've always been worried about this behaviour and I've always tried to make her stop doing it. Recently it's gotten even worse to the point where she'll even pinch her face.

I'm not equipped to help her with this because it probably stems from underlying mental issues, but I'm unsure of what type of specialist I should recommend her to see.

Any tips would be greatly appreciated.