Skin cancer is the most common of all cancers and accounts for about half of all cases in the US. The two main types are malignant melanoma and nonmelanoma skin cancers. Basal cell and squamous cell cancers account for most of the latter group. Although less common, melanoma skin cancers are far more dangerous, accounting for four percent of skin cancer cases but 79 percent of skin cancer deaths.

May is Skin Cancer Detection and Prevention Month, a time to focus on lowering your risk of developing skin cancer and on learning how to detect it early, when it is most treatable.

One of the most important steps in protecting yourself is to do a regular, thorough self-examination of your skin, Dr. Weinstock says. "Melanoma is a cancer that occurs right on the surface, where you can see it," he says. "But you can't see it if you don't look."

Finding melanoma, the more dangerous type of skin cancer, at an early stage is very important. There is a roughly 95 percent cure rate for patients whose melanomas are detected at one millimeter or less in thickness, but less than 50 percent of patients survive when their cancers are detected at four millimeters or more, Dr. Weinstock says.

To help people with skin self-exams, the ACS recommends a systematic way of looking at your skin. Dr. Weinstock describes the "Down and Back" method as follows:

• Start in front of a wall mirror. You should have a chair and a hand-held mirror. A good time for doing this is just after you step out of the shower.
• While standing, examine your face, chest and arms (both sides of the arms) and belly.
• Then, sit down to look at the front surfaces of your legs and feet. Use the mirror to examine the back of your legs and check out the soles of your feet.
• Stand up again and use the mirror to inspect your buttocks and upper back.

Dr. Weinstock recommends taking five to 10 minutes for this skin self-exam at least once a month. It also can help to have a partner, such as your spouse, help with places that are hard for you to see, such as your back, he says. "You need to do this thoroughly and you need to know what you're looking for," Dr. Weinstock says.

The ACS advises you to become familiar with birthmarks, moles and blemishes so that you know what they look like and can identify any changes in them. Signs to look for are changes in size, texture, shape and color of blemishes or a sore that does not heal.

The ABCD rule is a helpful guide to signs of melanoma. Notify your doctor about any of these signs:

• A is for asymmetry: Half of a mole or birthmark does not match the other half.
• B is for border: Edges are irregular, ragged, notched or blurred.
• C is for color: The color isn't the same all over but may have differing shades of brown or black, sometimes with patches of red, white or blue.
• D is for diameter: The area is larger than six millimeters (about the size of a pencil eraser) or is growing larger.