The body tans as a result of injury to the skin from Sun exposure.  That means that even a light tan is the result of an injury. Long-term Sun exposure results in aging of the skin. The skin can thin (atrophy), turn dark or light, be susceptible to easy bruising, tear easily, and sag. Tanning causes unwanted cosmetic changes known as premature aging of the skin and skin cancers.  So far, I have just referred to tanning from the Sun. Tanning beds also cause premature aging of the skin and skin cancers. As few as a dozen tanning bed exposures can result in an increase in risk for skin cancers years later.  Tanning beds use UVA and/or a combination of UVA/UVB.  It is known that UVA penetrates deeper in the skin-down to the level of superficial blood vessels. White blood cells (part of our immune system) circulate through those blood vessels. UVA actually paralyzes the white blood cells from effectively doing their duty of immune surveillance.  This can allow Sun damaged cells in the skin to take the next step to a skin cancer.  Statistics tell us that tanning bed users have an increase in skin cancers later on.  The incidence of Malignant Melanoma is definitely increased.