When we tan, melanocytes (skin cells) produce melanin, a pigment that protects our DNA from the harmful ultraviolet rays of the sun. Scientists have now discovered that the melanocytes also produce a light-sensitive element that accelerates tanning.
UVB rays increase melanin production within a few days of exposure to the sun. UVA rays, however, trigger this process within minutes. The reason is that UVA rays also cause melanocytes to produce rhodopsin, a light-sensitive molecule found in the retina, which, within 24 hours, multiplies the amount of melanin produced by five. This mechanism is our “emergency” defence system against aggression from the sun.