Yes, it is possible to contract a wide variety of STDs from oral sex, just like any other form of sex. Herpes is by far the most common when oral sex is concerned, but chlamydia, gonorrhea, HPV, HIV, and syphilis are all possible to contract when going down on your partner. If your partner does have an STD, you can always use a dental dam to stay protected. Having poor oral hygiene or open sores in the mouth also makes it easier to contract STDs during cunnilingus.