Skin cancer is an abnormal growth of skin cells. It most often develops on areas of the skin exposed to the sun’s rays. Skin cancer affects people of all colors and races, although those with light skin who sunburn easily have a higher risk.

Basal Cell Carcinoma

BCCs are abnormal, uncontrolled growths or lesions that arise in the skin’s basal cells, which line the deepest layer of the epidermis (the outermost layer of the skin). BCCs often look like open sores, red patches, pink growths, shiny bumps, or scars and are usually caused by a combination of cumulative and intense, occasional sun exposure.

BCC almost never spreads (metastasizes) beyond the original tumor site. Only in exceedingly rare cases can it spread to other parts of the body and become life-threatening. It shouldn’t be taken lightly, though: it can be disfiguring if not treated promptly.

More than 4 million cases of basal cell carcinoma are diagnosed in the U.S. each year. In fact, BCC is the most frequently occurring form of all cancers. More than one out of every three new cancers is a skin cancer, and the vast majority are BCCs.

Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is an uncontrolled growth of abnormal cells arising in the squamous cells, which compose most of the skin’s upper layers (the epidermis). SCCs often look like scaly red patches, open sores, elevated growths with a central depression, or warts; they may crust or bleed. They can become disfiguring and sometimes deadly if allowed to grow. More than 1 million cases of squamous cell carcinoma are diagnosed each year in the U.S., and (depending on different estimates) as many as 8,800 people die from the disease. Incidence of the disease has increased up to 200 percent in the past three decades in the U.S.

SCC is mainly caused by cumulative ultraviolet (UV) exposure over the course of a lifetime; daily year-round exposure to the sun’s UV light, intense exposure in the summer months, and the UV produced by tanning beds all add to the damage that can lead to SCC.

SCCs may occur on all areas of the body including the mucous membranes and genitals, but are most common in areas frequently exposed to the sun, such as the rim of the ear, lower lip, face, balding scalp, neck, hands, arms and legs. Often the skin in these areas reveals telltale signs of sun damage, including wrinkles, pigment changes, freckles, “age spots,” loss of elasticity, and broken blood vessels.

Melanoma

The most dangerous form of skin cancer, these cancerous growths develop when unrepaired DNA damage to skin cells (most often caused by ultraviolet radiation from sunshine or tanning beds) triggers mutations (genetic defects) that lead the skin cells to multiply rapidly and form malignant tumors. These tumors originate in the pigment-producing melanocytes in the basal layer of the epidermis. Melanomas often resemble moles; some develop from moles. The majority of melanomas are black or brown, but they can also be skin-colored, pink, red, purple, blue or white. Melanoma is caused mainly by intense, occasional UV exposure (frequently leading to sunburn), especially in those who are genetically predisposed to the disease. Melanoma kills an estimated 10,130 people in the US annually.

If melanoma is recognized and treated early, it is almost always curable, but if it is not, the cancer can advance and spread to other parts of the body, where it becomes hard to treat and can be fatal. While it is not the most common of the skin cancers, it causes the most deaths. In 2016, an estimated 76,380 of these will be invasive melanomas, with about 46,870 in males and 29,510 in women.