Skin cancer can occur anywhere on the body, but most commonly occurs in skin often exposed to sunlight. E.g. the face, neck, and hands. It especially occurs in fair-skinned and fair-haired people, those who had freckles as a child and those who have blue eyes.
There are 3 main types of skin cancer, which all begin in the epidermis:
Causes of skin cancer
Excessive UV-B exposure from sunlight causes all three skin cancer types.
Excessive UV-A exposure from sunlight. Now known to cause damage to proteins and lipids and DNA lesions by indirect (and possibly direct mechanisms), leading to carcinogenesis (Including cutaneous malignant melanoma) and aging skin. Link
Flat squamous cells form the outermost layer of the epidermis. Squamous cell carcinoma (SCC), a.k.a. "rat-bite" tumor, is diagnosed when these cells become abnormal and grow out of control. SCC sometimes develops from a precancerous skin growth called an actinic keratosis. SCC is usually seen as scaly red patches or open sores, which may crust and bleed. Characteristically it looks elevated with a central hole. Allowed to grow, it can be fatal.
Bowens disease is a form of squamous cell cancer in situ.
Most common type of cancer in the U.S. and the most common skin cancer . BCC is usually benign i.e. a relatively harmless skin cancer. Round basal cells reside under the squamous cells. Typically looks like a red patch, scar, shiny bump, pink growth or an open sore, which can bleed, ooze or crust. Rarely spreads or metastasizes, but should not be ignored since it is more easily treated whilst small.
In the lower epidermis, melanocytes produce melanin, the pigment that gives skin its color. Exposed to the sun, melanocyes make more pigment causing skin to darken.
Unrepaired DNA damages skin cells triggering mutations that cause skin cells to multiply rapidly and form malignant tumors. Curable if detected early, but each year in the U.S. ~10,000 people die of this type of cancer.
These are the signs to look for when examining tumors, which may indicate melanoma:
Asymmetrical: a line drawn through the middle of a tumor produces relatively similar halves;
Border: irregular or jagged, not smooth or ragged
Multicolored: A combination of colors is usual, one color tumors are probably OK
Diameter > 1/4 inch: non-malignant skin cancers tend to be smaller
Evolving: Changes in elevation, size, color, crusting, bleeding, itching, or anything else