Sexually transmitted infections (STIs) are spread through vaginal, anal, and oral sex with someone who has an STI.
Some sexually transmitted infections and diseases, like herpes and HPV, are spread by skin-to-skin contact — so you don’t actually have to “go all the way” (intercourse) to get one.
STIs are caused by certain bacteria, viruses, or parasites that spread through sexual activity. How they act differs—some don't even have symptoms so you could have or pass on an infection without knowing it.
There are many ways to reduce the risk...