But let's face it: Not everyone is going to follow this advice , particularly when it comes to oral sex. (Although the chance of STI transmission is lower for oral sex than it is for penetrative vaginal and anal sex, there's still a risk.) If you do have sex with multiple partners without using protection, the National Coalition for Sexual Health recommends you get tested for STIs at least once every six months. If you haven't been tested recently, it's also a good idea to tell prospective partners, so they can make an informed decision about the level of risk they're comfortable taking on.