Know the risks of unprotected sex Unprotected anal and vaginal sex is the most common way that HIV and STIs are passed on. It is important to keep yourself informed of the risks. Expand Using a condom is the best way to reduce risk of sexually transmitted infections and / or unwanted pregnancy. Alternatively there are other sexual activities, which do not carry the same risks as unprotected, penetrative sex, but can still be very pleasurable for you and your sexual partner(s). Information about specific sex activities and the risks they carry can be found on the NHS Choices website.