Most people nowadays know it's important to use a moisturizer every night. People with dry skin know this especially. But did you know it's important for people with oily skin to be using one consistently as well? Many times your skin is producing excess oil to hydrate and moisturize your skin. If you introduce a moisturizer into your routine it often times trains your skin to produce less oil. The basic function of moisturizers is to help treat your skin when it's dry and prevent it from drying out again. Moisturizers do this by holding water in the stratum corneum, the outermost layer of the skin. But they have other functions as well. They can help protect your skin from the environment because it creates a barrier on your skin that keeps oils from escaping and harmful outside elements from entering, causing dryness or irritation.