Understanding Skin Cancer -- the Basics

What Is Skin Cancer?

Picture of Skin Cancer Skin cancers involve abnormal cell changes in the outer layer of skin.

It is by far the most common cancer in the world, accounting for 75% of all cancer diagnoses. Most cases are cured, but the disease is a major health concern because it affects so many people. The incidence of skin cancer is rising, even though most cases could be prevented by limiting the skin's exposure to ultraviolet radiation.

Skin cancer is about three times more common in men than in women, and the risk increases with age. Most people diagnosed with skin cancer are between ages 45 and 54, although all forms of the disease are appearing more often in younger people. If you or any close relatives have had skin cancer, you are more likely to get the disease. Geography and race also factor into your chances of getting skin cancer, with the rate of skin cancer at its highest in places where fair-skinned Caucasians migrated from less sunny climes.

Every malignant skin tumor in time becomes visible on the skin's surface, making skin cancer the only type of cancer that is almost always detectable in its early, curable stages. Prompt detection and treatment of skin cancer is equivalent to cure.

Types of Skin Cancer

Skin cancers fall into two major categories: melanoma and nonmelanoma.

Melanoma can start in heavily pigmented tissue, such as a mole or birthmark, as well as in normally pigmented skin. Melanoma most commonly appears first on extremities, chest, or back, although it can occasionally arise on the palm of the hand; on the sole of the foot; under a fingernail or toenail; in the mucus linings of the mouth, vagina, or anus; and even in the eye.

Melanoma is a potentially aggressive, life-threatening cancer. It is readily detectable and usually curable if treated early, but it progresses faster than other types of skin cancer and can spread beyond the skin to affect numerous parts of the body, including the bones or brain. Once this occurs, melanoma becomes very difficult to treat and is incurable.


The two most common skin cancers, basal cell carcinoma and squamous cell carcinoma, are nonmelanomas and are rarely life threatening. They progress slowly, seldom spread beyond the skin, are detected easily, and usually are curable. Basal cell carcinoma, which accounts for nearly three out of four skin cancers, is the slowest growing. Squamous cell carcinoma is somewhat more aggressive and more inclined to spread. In addition, there are a few rare non-melanomas, such as Kaposi'ssarcoma, a potentially life-threatening disease characterized by purple growths; it is associated with a suppressed immune system and is almost always seen in patients with AIDS or the elderly.

Some noncancerous skin growths have the potential to become cancerous. The most common are actinic keratoses – crusty, reddish lesions that may scratch off but grow back on sun-exposed skin.


Who Is at Highest Risk for Skin Cancer?

Skin cancer tends to strike people of light skin color. Dark-skinned people are rarely affected and then only on light areas of the body, such as the soles of the feet or under fingernails or toenails. An estimated 40% to 50% of fair-skinned people who live to be age 65 will develop at least one skin cancer. The incidence of skin cancer is predictably higher in places with intense sunshine, such as Arizona and Hawaii. It is most common in Australia, which was settled largely by fair-skinned people of Irish and English descent.

What Causes Skin Cancer?

Excessive exposure to sunlight is the main cause of skin cancer. Sunlight contains ultraviolet (UV) rays that can alter the genetic material in skin cells, causing mutations. Sunlamps, tanning booths, and X-rays also generate UV rays that can damage skin and cause malignant cell mutations. Basal cell carcinoma and squamous cell carcinoma have been linked to chronic sun exposure, typically in fair-skinned people who spend considerable time outside. Melanoma is associated with infrequent but excessive sun exposure that causes scorching sunburns. One blistering sunburn during childhood appears to double a person's risk for developing melanoma later in life.

Fair-skinned people are most susceptible, because they are born with the least amount of protective melanin in their skin. Redheads, blue-eyed blonds, and people with pigment disorders such as albinism are at the greatest risk. But people with many freckles or moles, particularly abnormal-looking ones, may also be vulnerable to melanoma. Workers regularly exposed to coal tar, radium, inorganic arsenic compounds in insecticides, and certain other carcinogens are at slightly higher than normal risk for nonmelanoma skin cancer.


WebMD Medical Reference Reviewed by Stephanie S. Gardner, MD on July 27, 2015



American Academy of Dermatology: "Skin Cancer."

National Cancer Institute: "Skin Cancer."

American Cancer Society: "Skin Cancer: Basal and Squamous Cells" and "Melanoma Skin Cancer."

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