“Moving immediately into the shade does not stop sun damage, as UV rays can continue damaging skin cells hours after exposure,” The Guardian reports. Ultraviolet (UV) light is known to cause damage to DNA in skin cells, which increases the risk of the most serious type of skin cancer: melanoma. This study aimed to examine the biological mechanisms that may be involved in this process. Researchers used pigment-producing skin cells from mice (melanocytes) and found that it is the pigment melanin that plays a role in the damage process. Exposure to UV light causes melanin to produce small molecules, called cyclobutane pyrimidine dimers (CPDs). The CPDs form abnormal bonds between the “building blocks” in the DNA helix. These CPDs are formed at the time of UV exposure, but the research showed that the formation of CPDs also continues for three or more hours after UV exposure has stopped (“after dark”). After this, DNA repair mechanisms step in. (Source)