Yes, you can have sex when you're on your period.
There are a few risks associated with having sex while you or your partner are on their period. HIV and other sexually transmitted infections (STIs) may be passed on more easily, so you should always use a condom.
Also, while it's very unlikely, it's still possible to get pregnant if you have unprotected sex during your period. This is because some women ovulate early, and sperm can survive inside a woman's body for up to 7 days.