Anal-Oral?

"If a guy licks your butt, what are the risks?"

What you seem to be describing is anal-oral sex, also referred to as anilingus, rimming, rim-job, and a variety of other slang terms. It's performed by gay and straight people, and can provide a lot of pleasure as a consensual sex act. Anilingus involves kissing, licking, and sliding the tongue in and out of the anus.

Obviously this is not the cleanest part of the body, so clearly there's a risk of coming into contact with potentially harmful bacteria. If the lickee is infected with Hepatitis A, the licker is at risk of infection. Syphilis, herpes, gonorrhoea and chlamydia can also be transmitted through anilingus if either party is infected.

But there's a way to experience consensual anilingus safely, and that's to place a barrier between the lickee and licker. Dental dams (or a cut-up condom) are offer protection against infection. You could also use plastic wrap, but be sure it is *not* the microwaveable kind (this is porous!). Sex acts are as safe as you make it!