Suntanning

Melanocytes are the skin cells that produce melanin, the brown pigment that gives each person their genetically-determined baseline skin color. Except in redheads (whose skin typically does not produce the normal brown melanin) melanocytes are capable of increasing or decreasing the amount of melanin pigment they produce, with an increase above baseline manifesting as a suntan. You might wonder, how does sun exposure induce the melanocyte to make more melanin? The sun’s UV rays are a form of energy, and when they are absorbed by the skin, that energy can damage the cell’s DNA. In keratinocytes, which are the major cell type of the skin’s epidermis (top layer), DNA damage is recognized by surveillance proteins inside the cell that react when they detect it. These surveillance proteins set two responses in motion. They initiate repair of the damaged DNA and simultaneously stimulate melanocytes to increase melanin pigment production. Melanin absorbs UV rays like a sunscreen does. In white skin, this response that upregulates melanin production is a brilliant biologic strategy which aims to produce a shield against additional incoming UV radiation, and protect the keratinocytes from further damage. During the 20^th century, a suntan was generally regarded as healthy, attractive, and desirable. Now that we understand the biology of a suntan, namely that it’s a defensive reaction to DNA damage, it certainly should not be regarded as healthy. In truth, a suntan reveals skin that has been damaged and now has an increased risk of developing skin cancer.