text: are condoms 100%safe? if not why arent they?also if not why do we use them?   condoms are definitely not 100% safe against pregnancy or any std's. they aren't 100% safe because they can break or slip off during intercourse or they can have a flaw (tiny hole) from when they were manufactured. people use them because they do offer some protection (very little protection against pregnancy), but they should be used in combination with other protection. =-)