WHAT IT IS: A wrinkle, also known as a rhytide, is a fold, ridge or crease in the skin. There are a few different types of wrinkles: dynamic wrinkles, static wrinkles, and wrinkle folds. With age, skin cells divide more slowly, and the skin’s inner layer, called the dermis, begins to thin. That starts to undo skin’s stretchiness and structure. Aging skin also starts to lose its ability to hold on to moisture, makes less oil, and is slower to heal. That all contributes to the wrinkling process. Although genetics mainly determine skin structure and texture, sun exposure is a major cause of wrinkles, especially for fair-skinned people. Other factors, such as pollutants and smoking, also contribute to lines and wrinkles.