If both you and your partner have tested negative for all STIs and neither of you has had sex with another partner since testing, you cannot get an STI unless one of you received a false negative result (one of the tests showed negative even though you or your partner had an infection).  The main way to get an STI is to have sex with another person who has not tested negative for all STIs after having sex with someone else. Some STIs, like herpes, can be passed on by skin-to-skin contact even when you’re not having sex. If you get symptoms of an STI, you and your partner should get tested. STI tests are very accurate when taken at the right time, but in rare cases you can get a false negative. If you take an STI test less than 2 weeks after unprotected sex, you may not get accurate results.