The sunlight that reaches us is made up of two types of harmful rays: long wave ultraviolet A (UVA) and short wave ultraviolet B (UVB). UVA rays penetrate deep into the dermis, the skin's thickest layer.
Unprotected exposure can lead to premature skin aging and wrinkling (photoaging), and suppression of the immune system. UVB rays will usually burn the superficial layers of your skin. It plays a key role in the development of skin cancer. The intensity of UVB rays vary by season, location and time of day, with 10AM to 4PM being the peak hours. Sunburned skin doesn't just feel awful, it can cause permanent damage over time.