Bruising happens when blood pools in your skin, outside of your blood vessels. As you age, you lose subcutaneous fat and collagen under the top layer of skin. This can make your blood vessels more susceptible to trauma — causing you to bruise more often. "Think of styrofoam peanuts around crystal glasses, where the peanuts are the collagen and subcutaneous fat, and the glasses are your blood vessels," Los Angeles-based dermatologist Dr. Rebecca Fitzgerald tells BuzzFeed Life. "When there's not as much packing the blood vessels in, you tend to get injured from more minor traumas."