Only abstinence is 100% safe. But when you decide to have sex you can make it as safe as possible, taking precautions against unwanted pregnancy and Sexually Transmitted Diseases.
If you want to prevent pregnancy, use another form of birth control in addition to a condom, like the pill, a diaphragm, the nuvaring or an IUD. Of the girls who are sexually active who use only condoms 2-12% becomes pregnant every year, so that’s not really safe.
You can reduce the risk of getting a STD by always using a condom and by limiting the number of partners you have sex with.
If you see blisters, a cold sore or genital warts on your partner’s genitals don’t have sex. A condom might not provide enough protection.
With anal intercourse you should use a condom that’s especially made for this purpose.
Giving oral sex always use a (flavoured) condom or a dental dam. Don’t get semen or menstrual blood in your mouth (this is risky in connection with HIV).
Often there are no symptoms. So your lover can be infected without knowing it, thus being unaware of putting you at risk. That’s why you have to use condoms every time you have sex. You can only do without condoms if both of you are still virgins. But in that case you must be sure your lover is not telling lies.