Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Sun Exposure ?
    ### Response:
    Ultraviolet (UV) rays are an invisible form of radiation. They can pass through your skin and damage your skin cells. Sunburns are a sign of skin damage. Suntans aren't healthy, either. They appear after the sun's rays have already killed some cells and damaged others.
    