Skin cancer is a disease in which malignant (cancer) cells form in the tissues of the skin.
The skin is the body's largest organ. It protects against heat, sunlight, injury, and infection. Skin also helps control body temperature and stores water, fat, and vitamin D. The skin has several layers, but the two main layers are the epidermis (upper or outer layer) and the dermis (lower or inner layer).
The epidermis is made up of 3 kinds of cells:
Squamous cells are the thin, flat cells that...
Basal cell carcinoma and squamous cell carcinoma are the most common forms of skin cancer but have substantially better prognoses than the less common, generally more aggressive melanoma.
Nonmelanoma skin cancer is the most commonly occurring cancer in the United States. Its incidence appears to be increasing in some  but not all  areas of the United States. Overall U.S. incidence rates have likely been increasing for a number of years. At least some of this increase may be attributable to increasing skin cancer awareness and resulting increasing investigation and biopsy of skin lesions. A precise estimate of the total number and incidence rate of nonmelanoma skin cancer is not possible, because reporting to cancer registries is not required. However, based on Medicare fee-for-service data extrapolated to the U.S. population, it has been estimated that the total number of persons treated for nonmelanoma skin cancers in 2006 was about 2,152,500.[3,4] That number would exceed all other cases of cancer estimated by the American Cancer Society for that year, which was about 1.4 million.
Melanoma is a reportable cancer in U.S. cancer registries, so there are more reliable estimates of incidence than is the case with nonmelanoma skin cancers. In 2013, it is estimated that 76,690 individuals in the United States will be diagnosed with melanoma and approximately 9,480 will die of it. The incidence of melanoma has been increasing for at least 30 years. From 2005 to 2009, melanoma mortality rates decreased in whites younger than 50 years by 2.8% per year in men and by 2.0 % per year in women. However, the rates have been increasing by 1.1% per year in white men aged 50 years and older, and have been stable in white women aged 50 years and older during this same time period.
A study of skin biopsy rates in relation to melanoma incidence rates obtained from the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute indicated that much of the observed increase in incidence between 1986 and 2001 was confined to local disease and was most likely caused by overdiagnosis as a result of increased skin biopsy rates during this period.
Epidemiologic evidence suggests that exposure to UV radiation and the sensitivity of an individual's skin to UV radiation are risk factors for skin cancer, although the type of exposure (high-intensity and short-duration vs. chronic exposure) and pattern of exposure (continuous vs. intermittent) may differ among the three main types of skin cancer.[7,8,9] In addition, the immune system may play a role in pathogenesis of skin cancers. Organ-transplant recipients receiving immunosuppressive drugs are at elevated risk of skin cancers, particularly squamous cell cancers (SCC). Arsenic exposure also increases the risk of cutaneous SCC.[10,11]