Classification of skin types is based on individual response after the first exposure for 30 minutes at mid-day sunlight. Thus there are 6 phototypes( after Fitzpatrick ‘scale)regardeling the skin responses to ultraviolet, the skin tends to tan or, conversely, to suffer sunburn:
Type I – people with very white skin, redheads, with blue or green eyes, with or without freckles. They never get tanned, but always get sunburns;
Type II – people with white skin, blue eyes, blond or brown hair, which often burn in the sun and sometimes difficulty get tanned;
Type III – people with brown eyes and hair, which sometimes burn in the sun and get tanned;
Type IV – people with black hair and dark eyes and brown, which always get tanned and never burn in the sun, except from extreme conditions;
Type V – people with a moderate constitutional pigmentation (Mediterraneans, Asians, Metis), who get easily and more tanned, but do not burn;
Type VI – people with marked constitutional pigmentation (Blacks), which do not burn.
Persons belonging to types V and VI may burn only during prolonged exposure to sunlight, but not experience side effects after 30 minutes.
Sun exposure can cause varying degrees of actinic erythema (redness) which may be followed by edema (swelling) and flictene (blisters) and then a descuamation. Ultraviolet A (UVA), which are predominant in intensity and duration, are present throughout the day and throughout the year, causing fast redness and skin pigmentation (tanning). Ultraviolet B (UVB), present at noon (in hours 11-16) especially in summer, causing sunburn slower 12-24 hours after exposure.
Overall, one can say that ultraviolet B (UVB) affects only the superficial layers of skin, is responsible for sunburn and skin cancer production (by affecting cellular DNA). Ultraviolet A (UVA) penetrate deeper into the skin and triggers the production of melanin, the pigment that colors skin. They are responsible for premature skin aging. And they are incriminated in producing skin cancer. Center for Research on Cancer in the UK says that sunburn is significantly linked to skin cancer. A strong produced sunburn before the age of 20 years doubles the risk of developing melanoma.