TweetHmmm....never heard of anything like this. If it was at an injection site it could be linked to his injection methods, but with it being on his cheeks, I have no idea!!!
As far as letting him know about the dangers of improper AAS use, find some articles of proper use and print them out for him or send him the links for him to read. You can also send him articles of people gettiung hurt. Send him a link of Greg Valentino, if that doesn't scare him, then it's a lost cause!!!