It is extremely unlikely that you would get a sexually transmitted infection from putting your mouth on a vulva (external genitals of someone that does not have a penis). By the way, this sexual activity is called ‘cunnilingus’. We do not believe that gonorrhea or chlamydia are transmitted that way and you cannot get HIV from performing oral sex on a vulva. It is theoretically possible to get syphilis from performing oral sex on a vulva but that is very rare. If you wish to protect yourself, you can use a barrier (a ‘dental dam’, a thin square of latex) between your mouth and your partner’s vulva.