At night, your skin kicks into catabolysis -- a renewal mode where more blood circulates, cell debris is removed and recycled, and your skin repairs all the damage of the day. When you don't sleep, your skin is forced to skip the catabolysis stage, meaning your face holds all onto inflammation, debris, free radicals and puffiness and literally ages faster. Hey, it's called beauty sleep for a reason. Studies show that poor sleepers have more wrinkles, uneven tone and less elasticity than those who hit the hay. Sleeping is basically the easiest anti-aging remedy ever.

If you're pulling an all-nighter, you're not doing it in the dark, and several studies have found that women exposed to artificial light at night (particularly night shift workers) develop breast cancer at a higher rate than other women. The research is so convincing, the World Health Organization has labeled night shift work a probable carcinogen. Researchers believe the phenomenon is linked to melatonin, the hormone that controls your sleep and wake cycles. Melatonin levels decrease when light is present, and melatonin is also partly responsible for suppressing estrogen. Scientists say less melatonin means more estrogen, which increases breast cell production. More breast cells mean more possibilities for abnormal (breast cancer-causing) cells.