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.
However it was not until 1889 that the first human case was described by Levinson when he found the Gnathostoma larva in an infested Thai woman. The lifecycle of G. spinigerum was described by Svasti Daengsvang and Chalerm Prommas from Thailand in 1933 and 1936. This delay in identification of the parasite in humans is due to the fact that humans are not a definitive host for this parasite making infection from this parasite rare. Gnathostomiasis infection is rare because the parasite must be digested when it has reached its third larvae stage, providing only a short time frame in which the parasite is capable of infecting humans. It is uncommon for the larvae to penetrate the skin of individuals exposed to contaminated food or water without ingestion. See also
List of parasites (human)
List of migrating cutaneous conditions

References
External links
Gnathostomiasis Archived 2013-02-15 at the Wayback Machine at CDC
Gnathostomiasis at eMedicine