Ladies, be honest: Do certain aspects of sexual activity sometimes gross you out? If you answered yes, you’re not alone, and there’s a psychological and physiological explanation for why you might feel that way. Both sex and disgust are core aspects of human experience. Scientists believe that disgust evolved as a defensive mechanism to keep us from being contaminated by external sources.1 Accordingly, the mouth and the vagina, two body parts that lie at the border of the body (and are therefore at a higher risk for contamination), demonstrate greater disgust sensitivity; for example, we are likely to be especially grossed out by having a spider crawling on/around the mouth or vagina compared to, say, the left arm.2 Add to this the finding that some of the strongest triggers for disgust are body odor, saliva, semen, and sweat, all heavily involved when getting “down and dirty,” and you can see how the relation between sex and disgust seems contradictory or even obstructive. In fact, you might be left wondering how humans manage to have pleasurable sex at all!