CoffeeAndMilk When it comes to skincare, it can often seem like hydration is the end-all and be-all. Beyond the myriad benefits it offers to common concerns, like aging and acne, hydration is what gives way to that dewy glow that we all dream of. But, the flipside is the much-dreaded oily skin, which is not necessarily a bad thing, can feel like a stubborn enemy that persists no matter what you do. “Oily skin occurs when the sebaceous glands produce an excess of sebum, or oil, resulting in skin that is greasy, shiny, and more acne-prone,” explains Dendy Engelman, MD, a board-certified dermatologist in New York City. There are many reasons skin might turn oily, but much of it ultimately boils down to your biology. “Genetics and age play a role in how oily your skin is; if oily skin runs in your family, you may have it too,” the dermatologist says, noting that younger skin, especially during teenage years, also tends to be oilier than mature skin.