Prefer a sharp wing or a dark, defined line to the more subtle smoky eye? If you've got a mascara tube and a thin brush, you've got all you need. Glide your makeup brush carefully along the mascara wand to pick up the color and then apply the brush to your eyes the same way you would with gel eyeliner (via Women's Health). P.S., the cool thing about eyeliner and mascara is they can pretty much serve as each other's back-ups in a makeup emergency — you also can use eyeliner when you can't find your mascara!

There's one item in your beauty arsenal that you should never, ever use in place of eyeliner, though, even though it looks almost exactly like an eye pencil: your lip liner. Even a dark brown lip liner that's almost the exact same shade as what you use on your eyes is forbidden. That's because lip liner contains additives that are not meant to be used near the delicate organs that are your eyes. 

"Using unapproved colorants around your eye could even lead to blindness," cosmetic chemist Randy Schueller told Allure. "Colors intended for use around the eye have to be specially approved by the FDA."