The four known types of OCA are caused by mutations in the TYR, OCA2, TYRP1, and SLC45A2 genes. Age
In hominids, the parts of the body not covered with hair, like the face and the back of the hands, start out pale in infants and turn darker as the skin is exposed to more sun. All human babies are born pale, regardless of what their adult color will be. In humans, melanin production does not peak until after puberty.The skin of children becomes darker as they go through puberty and experience the effects of sex hormones. This darkening is especially noticeable in the skin of the nipples, the areola of the nipples, the labia majora in females, and the scrotum in males. In some people, the armpits become slightly darker during puberty. The interaction of genetic, hormonal, and environmental factors on skin coloration with age is still not adequately understood, but it is known that men are at their darkest baseline skin color around the age of 30, without considering the effects of tanning. Around the same age, women experience darkening of some areas of their skin.Human skin color fades with age. Humans over the age of thirty experience a decrease in melanin-producing cells by about 10% to 20% per decade as melanocyte stem cells gradually die. The skin of face and hands has about twice the amount of pigment cells as unexposed areas of the body, as chronic exposure to the sun continues to stimulate melanocytes.
Tanning involves not just the increased melanin production in response to UV radiation but the thickening of the top layer of the epidermis, the stratum corneum.A persons natural skin color affects their reaction to exposure to the sun. Generally, those who start out with darker skin color and more melanin have better abilities to tan. Individuals with very light skin and albinos have no ability to tan. The biggest differences resulting from sun exposure are visible in individuals who start out with moderately pigmented brown skin: the change is dramatically visible as tan lines, where parts of the skin which tanned are delineated from unexposed skin.Modern lifestyles and mobility have created mismatch between skin color and environment for many individuals. Vitamin D deficiencies and UVR overexposure are concerns for many. It is important for these people individually to adjust their diet and lifestyle according to their skin color, the environment they live in, and the time of year. For practical purposes, such as exposure time for sun tanning, six skin types are distinguished following Fitzpatrick (1975), listed in order of decreasing lightness:

Fitzpatrick scale
The following list shows the six categories of the Fitzpatrick scale in relation to the 36 categories of the older von Luschan scale:
Dark skin with large concentrations of melanin protects against ultraviolet light and skin cancers; light-skinned people have about a tenfold greater risk of dying from skin cancer, compared with dark-skinned persons, under equal sunlight exposure.