Skin cancers are cancers that arise from the skin. They are due to the development of abnormal cells that have the ability to invade or spread to other parts of the body.^[1] There are three main types: basal-cell skin cancer (BCC),squamous-cell skin cancer (SCC) and melanoma.^[2] The first two together along with a number of less common skin cancers are known as nonmelanoma skin cancer (NMSC).^[3][4] Basal-cell cancer grows slowly and can damage the tissue around it but is unlikely to spread to distant areas or result in death.^[3] It often appears as a painless raised area of skin, that may be shiny with small blood vessel running over it or may present as a raised area with an ulcer.^[2]Squamous-cell cancer is more likely to spread.^[3] It usually presents as a hard lump with a scaly top but may also form an ulcer.^[5] Melanomas are the most aggressive. Signs include a mole that has changed in size, shape, color, has irregular edges, has more than one color, is itchy or bleeds.^[6]

Greater than 90% of cases are caused by exposure to ultraviolet radiation from the Sun.^[7] This exposure increases the risk of all three main types of skin cancer.^[7] Exposure has increased partly due to a thinner ozone layer.^[3][8]Tanning beds are becoming another common source of ultraviolet radiation.^[7] For melanomas and basal-cell cancers exposure during childhood is particularly harmful.^[9] For squamous-cell cancers total exposure, irrespective of when it occurs, is more important.^[7] Between 20% and 30% of melanomas develop from moles.^[9] People with light skin are at higher risk^[2] as are those with poor immune function such as from medications or HIV/AIDS.^[3][10] Diagnosis is bybiopsy.^[6]

Decreasing exposure to ultraviolet radiation and the use of sunscreen appear to be effective methods of preventing melanoma and squamous-cell cancer.^[9][11] It is not clear if sunscreen affects the risk of basal-cell cancer.^[11]Nonmelanoma skin cancer is usually curable.^[3] Treatment is generally by surgical removal but may less commonly involve radiation therapy or topical medications such as fluorouracil.^[2] Treatment of melanoma may involve some combination of surgery, chemotherapy, radiation therapy, and targeted therapy.^[6] In those people whose disease has spread to other areas of their bodies, palliative care may be used to improve quality of life.^[6] Melanoma has one of the higher survival rates among cancers, with over 86% of people in the UK and more than 90% in the United States surviving more than 5 years.^[12][13]

Skin cancer is the most common form of cancer, globally accounting for at least 40% of cases.^[3][14] It is especially common among people with light skin.^[15] The most common type is nonmelanoma skin cancer, which occurs in at least 2-3 million people per year.^[9][16] This is a rough estimate, however, as good statistics are not kept.^[2] Of nonmelanoma skin cancers, about 80% are basal-cell cancers and 20% squamous-cell cancers.^[4] Basal-cell and squamous-cell cancers rarely result in death.^[9] In the United States they were the cause of less than 0.1% of all cancer deaths.^[2] Globally in 2012 melanoma occurred in 232,000 people, and resulted in 55,000 deaths.^[9] Australia and New Zealand have the highest rates of melanoma in the world.^[9] The three main types of skin cancer have become more common in the last 20 to 40 years, especially in those areas which are mostly Caucasian.