Overall skin coloration is determined by the degree to which cells in the skin called melanocytes produce the pigment melanin. Melanin is also responsible for hair and eye coloring. The subtype pheomelanin is responsible for red hair, while the subtype eumelanin is responsible for grey, black, yellow, and brown hair. People with certain ancestries have the genetic coding to create a lot of melanin in their skin and therefore have dark skin. Albinism occurs in individuals who produce no melanin. Freckles are small bunches of melanin that are visible on individuals with fair skin. The gene for the melanocortin-1 receptor (MC1R) plays a role in the presence of freckles; individuals with the dominant variant of MC1R have freckles. The technical word for normal, flat freckles that are a shade of red or brown is ephelides. The concentrations of melanin that are responsible for freckles are much different than clusters of melanocytes, which is associated with skin cancer. People with freckles have a normal number of melanocytes; their melanocytes just create clusters of melanin.
Melanin has an extremely important role- it absorbs UV light and dissipates the UV rays as heat. This process protects our DNA from the damage that can be imparted by UV rays. Individuals with dark skin have more UV-dissipating capacity. This important function of melatonin is appreciated throughout nature. Melanin can be found all over nature from bacteria to humans, with the curious exception of spiders. Sunlight is therefore a stimulus for melanocytes to produce melanin because they are trying to protect the body from UV rays. The increased production of melanin that occurs after melanocytes are exposed to sunlight results in a suntan- or the darkening of freckles. Because newborn babies haven’t been exposed to sun, they not have freckles and the use of sunscreen or the clothing protection can prevent freckles. Repeated exposure to the sun throughout life can result in liver spots, which are basically permanent freckles that do not fade away. Reverse freckles, or white freckles, are simply spots of no melanin.
Some people try to get rid of freckles through a bleaching process involving an agent such as hydroquinone that slows down the process at which melanocytes produce melanin. There is an autoimmune condition called vitiligo in which melanocytes are attacked by the immune system and become too weak to produce melanin. The result is patches of white skin and eventual whitening of areas of the body. This is what happened to Michael Jackson.