Need some helping with helping a friend...

Hello, This may be a bit of an unorthodox question. I have a friend who has this problem, or at least I think it's a problem. My friend is constantly squeezing at pimples, and sometimes I'm not even sure if there's one there. Because of his vigorous squeezing, there is an open sore left. Then he will pick at the scab for weeks, and now (in the last month or so) he has started eating the scabs. My friend suffers from a chronic illness which has made his kidneys not function properly, to the point where he regularly attends dialysis. This, and the medication he takes, has made his immune system weak. It also makes him prone to blood infections, and he's already had a few. The reason I'm here is I would like to speak to my friend about his problem, but I do not know if there is a "proper" way to broach the subject. I want to do this for his well being. The only other reason I'm pressed to approach him about this issue is that he exhibits this behavior in public - restaurants, bars, any social gatherings - and picks primarily at his arms and face. We live in a small community, my friend has no family to support him, and he really enjoys spending time with people in the community and his network of friends. I am worried for both his health, and worried that his problem might alienate him from those around them. I'm not sure if it's helpful information, but some people have confronted him about his behavour while he's doing it and his response is always to deny that he's doing it. Or he says that he is itchy and that he has accidentally scratched off the scabs. Lastly, I hope I do not offend anyone inadvertently with this post. It is not my intention to judge or make assumptions. I just want to help out a friend and I want to do it with more knowledge than less. :X Thank you for reading