Sex can be loads of things - fun, exciting, thrilling, warm, funny. It's also risky. If you aren't careful you could catch a Sexually Transmitted Infection (STI). There are zillions of them, find out here about the common ones.

A lot of the time you can't tell if someone has one - often the person who has it doesn't even know because there are no signs. An STI can stay hidden for years and years and rear its ugly head in the future.