QUESTION
When giving a man a blow job, am I any safer (STD-wise) if I spit instead of swallow his ejaculate?

ANSWER
Oral sex and swallowing semen carry a very low risk of HIV infection. There are definitely case reports and individual experiences that suggest HIV can be transmitted through oral sex, although it is much less likely than via unprotected anal sex. It may be possible to take this concept further and reduce an already low-risk activity to a lower-risk one (the thinking would be that no semen would be safer than some). But truthfully, there is no scientific proof in this area yet.

However, you can get other STDs from giving a blow job to an infected partner. Syphilis, shigella (if the receiver has just topped someone else), gonorrhea and Hep A can be transmitted during unprotected oral sex. These are not necessarily dependent on whether you spit or swallow. All of these STDs are three to five times more likely to be transmitted to the giver if either partner is HIV+. Learn what risks you are taking when engaging in particular sexual activities.

To your health,
Dr. K