Sexually transmitted infections (STIs), or sexually transmitted diseases (STDs), are infections that are passed from one person to another through sexual contact. They are usually spread during vaginal, oral, or anal sex. But sometimes they can spread through other sexual contact involving the penis, vagina, mouth, or anus. This is because some STIs, like herpes and HPV, are spread by skin-to-skin contact.

Some STIs can be passed from a pregnant person to the baby, either during pregnancy or when giving birth. Other ways that some STIs may be spread include during breastfeeding, through blood transfusions, or by sharing needles.