Albeit looking harmless, actinic keratosis can develop into squamous cancer. It is more common in old people.
Red hair and blue eyes are associated with a highly· and moderately· increased risk of melanoma respectively.
Fair complexion is another risk factor, but the degree of association with melanoma depends on the age of the patient. In patients over the age of 45 years, fair skin can be as significant a risk factor as multiple nevi.
Here is chart for estimating melanoma risk in a person:
Exposure to ultraviolet radiation(UVR) is a critical factor in the development of sun-related melanomas. Ultraviolet A(UVA), wave length 320·400 nm, and ultraviolet B (UVB), 290-320 nm, potentially are carcinogenic and actually may contribute to induce a melanoma. The suggested mechanisms through which UV exposure can play its role are:
Suppression of the immune system of the skin
Induction of melanocyte cell division
Free radical production
Damage of melanocyte DNA
Interestingly, melanoma does not have a direct relationship with the amount of sun exposure because it is more common in white·collar workers than in those who work outdoors. Also it is more common on the back of men and lower leg of women, when there is no significant sun exposure.