Symptoms

Melanoma. Use the American Academy of Dermatology's ABCD rule if you see a suspicious mole that changes in any of the following ways:

• A: Asymmetry -- one half is unlike the other half.
• B: Border irregularity -- scalloped or irregular borders.
• C: Color -- varied from one area to another; shades of tan and brown; black; sometimes white, red or blue.
• D: Diameter -- larger than the diameter of a pencil eraser, about ¼ of an inch or 6 millimeters.

Also, look for a mole that:

• Oozes, bleeds, is scaly, or gets a sore in or around it.
• Seems to spread to nearby skin.

Basal cell carcinoma can occur anywhere on the skin, but the most dangerous lesions tend to form on the face, on or near the nose or corners of the eyes. Look for these features:

• Single red, pearly (shiny) bump.
• Single plaque (flat area) with clearly defined margin.
• Tendency to bleed, scab up and heal.
• Sunken middle portion that may look like a scar or ulcer (red, like an open wound).

Squamous cell carcinoma usually occurs on sun-exposed skin from a precancerous lesion, chronic sore or scar. Look for these features:

• Usually a single red, yellowish or brown lesion.
• Thick, scaly, "wart-like," irregular surface.
• Tends to become raised and firm.
• Cracking or peeling of the lower lip that is not helped by lip balm.

More on Skin Cancer

In the Encyclopedia:

This article was reviewed and updated June 2007.