There are two types of UV rays: UVB and UVA. Both can play a part in skin cancer formation, premature skin aging, and other forms of skin damage. UVB rays penetrate the outer layer of the skin causing damage to skin cells and are the primary cause of sunburn and skin cancer. UVA rays can pass through window glass and penetrate deeper layers of the skin than UVB. UVA rays contribute to premature signs of aging, including fine lines and wrinkles, and skin cancer.