Hmmm....that's a tricky thing to bring up. If it's a friend, significant other or colleague, you could casually bring it up in a conversation. Perhaps you could start talking about hair, and then mention how a while ago you noticed that you had developed dandruff...don't forget to tell them how you learned to check for it...then talk about how you "fixed" the problem. This way you're planting the idea, but not injuring the person if you don't know them well enough to be direct. What do you think?