Skin cancers, whether they are basal cell carcinoma (BCC), squamous cell carcinoma (SCC) or melanoma, can have a number of causes. Exposure to sunlight and damage caused by severe sunburns or tanning beds is perhaps the best-known cause of epidermal malignancy, but medications, age, skin pigmentation, and even geographic location can all influence an individual’s susceptibility to these diseases.
UVA and DNA Mutations. Exposure to sunlight has been linked to epidermal skin cancer for many years. Ultraviolet light in sunlight can cause DNA in the epidermis—the outer layer of the skin—to mutate.
Sunlight contains two different forms of ultraviolet light, both of which have been linked to tumor development: UVA and UVB. UVA has a longer wavelength, and penetrates deeper into the skin. UVB is absorbed directly into the epidermis, and is the primary cause of severe sunburns.
UV light causes mutations in DNA strands, which are then reproduced during cell replication. These mutations are generally considered to be the starting point for epidermal cancer. Specific genetic changes have been linked to SCC, BCC and melanomas:
squamous cell carcinoma: mutations to the p53 gene
basal cell carcinoma: changes to the PATCHED gene
melanomas: mutations to the p16 gene.
Long-term exposure to UV rays is seen as the primary cause of SCC and BCC. Chronic exposure can also cause melanomas, but not with the same frequency as the non-melanoma skin cancers. Instead, intermittent exposure, such as severe sunburns during childhood, seems to predispose an individual for melanomas.
Immunosuppression. Ultraviolet rays may damage epidermal Langerhans cells, which are part of the body’s immune system. Damage to the immune system increases the chance of many types of cancer.
This finding has been confirmed by the high rate of epidermal skin cancers associated with organ transplantation. After an organ transplant, immunosuppression medications must be used to prevent organ rejection. As a result of these medications, the immune system’s ability to defend the body against infection and malignancy is significantly compromised.
Research from both Australia and the Netherlands indicates that skin cancer incidence rates rise anywhere from forty to seventy percent after twenty years of immunosupprerssion therapy. In Australia, where high levels of solar radiation penetrate the ozone layer, the incidence rate for skin cancer in transplant patients is 45 percent after eleven years.
Skin Pigmentation, Freckles and Melanin. Ethnicity and skin type play a role in how susceptible an individual is to epidermal skin cancers. Caucasians are most at risk, especially people with very fair skin, red or blonde hair, and blue eyes. Freckles, particularly on the upper back, also increase risk levels. The levels of melanin produced by melanocytes determine skin pigmentation. Darker-skinned people have more melanin than lighter-skinned individuals. People of African decent are least likely to develop cancers of the epidermis.
Skin Types and Sun Exposure
Different skin types determine how sensitive you are to sun exposure, and how likely you are to develop severe sunburns.
Type I: never tans, suffers severe sunburns easily
Type II: barely tans, burns quickly
Type III: tans to light brown, burns after moderate exposure
Type IV: tans brown, has reasonable resistance to burns
Type V: hardly ever burns, dark tans when in sun
Type VI: never burns, and has dark pigmentation.
Note that no matter how high your resistance to the sun might be, excessive sun exposure increases your risk of developing skin cancer.
This warning also applies to the use of tanning beds and other UV lights.
Most epidermal skin cancers are diagnosed after age fifty. However, many years of damage occur before the cancer develops. Chronic exposure to sunlight and severe sunburns before the age of ten increase the lifelong chance of developing skin cancer.
Geographic location is another important factor. Fair-skinned individuals in hot climates such as Australia are at greater risk than they are in more temperate climates. People such as fishermen and farmers whose jobs or leisure activities require them to be outside most of the time, are also at higher risk than the rest of the population.
Other factors include:
family history of melanoma