Waterproof mascara is the sensible choice if you're in the heat, going swimming or your lashes brush against your skin (meaning natural oils can pass on to the lashes and smudge mascara). But beware the after-effects. Because waterproof mascara is so difficult to remove, remnants might remain once you've moved back to normal mascara. These can clog up lashes or continue to smudge or flake long after you've tried to get it all off. So steer clear in the run-up to an important day when you want your eyes to look their best with traditional mascara.