If you are sexually active, particularly if you engage in unprotected sex, you are vulnerable for getting and (STD). Regardless of whether you are straight or gay, married or single, whether you engage in oral, anal or vaginal sexyou're vulnerable to getting an STD infection. If untreated, STDs can increase your risk of acquiring another STD such as HIV. This happens because an STD can stimulate an immune response in the genital area or cause sores, either of which might make HIV transmission more likely. Some untreated STDs can also lead to infertility.