[Pi.R^2]

Apologies for going on a slight tangent, but I think I disagree with you a bit Hannah (Serendipity). For a service user who struggles with self harm, it could be positive for them to see someone working in mental health who has old scars, as that tells them that it is possible to stop self harming and that a history of self harm doesn't stop you getting a great job. Though I completely see that it could also have the negative effect of being triggering and of course it's always up to the individual whether or not they want to cover up. [/tangent].

Hannah (Charmed), I don't think it's unprofessional. I recently started a new job in a secondary school with no air-conditioning and I was too hot to really do my job properly so I spoke to the deputy head teacher and she had no problem with me wearing short sleeves when necessary, so that confirmed to me that it's not unprofessional which was a big concern of mine. We discussed how best to answer any potential questions, and I plan to go for "gosh, that's quite a personal question" and refocus them on what they're supposed to be doing (maths and not asking me personal questions). I know another RYLer who says "I got hurt when I was little, but don't worry, I'm OK now" for primary children. Perhaps you'd find either of those helpful, depending on the age and level of understanding of the person asking.

In terms of adult colleagues, they should really know better and I'd be tempted to say something sarcastic like "I fell in a blender" (also an excuse stolen from another RYLer!).

Sorry for such a ramble. tl;dr I don't think it's unprofessional and you may find it helpful to have an answer 'prepared' for if people do ask.