The vast majority of skin cancers could be prevented by routinely shielding your skin from the sun's damaging ultraviolet (UV) rays. Yet most Americans aren't doing enough to protect themselves. They only use sunscreen at the pool, or forget to reapply, or forget about wearing hats, long-sleeved shirts, and staying in the shade.

This May, Skin Cancer Detection and Prevetnion Month, bring your sun-protection habits up to date.

Dermatologists recommend doing a skin check monthly, so you'll be more likely to notice any changes or even find a skin cancer when it's still small. If you haven't picked up this habit, now is the time to start. Be sure to examine your palms, fingernails, and feet, too. Although most skin cancers develop in areas that get lots of sun exposure, tumors may also affect these body parts.

Check yourself in a well-lighted room using both a full-length mirror and a hand-held mirror. Become familiar with your birthmarks, moles, and blemishes so you know what they usually look like. That way you'll be able to identify any changes more easily. Look for any changes in size, texture, shape, and color of blemishes, or a sore that does not heal. Get your spouse or partner to help you check those hard-to-see places. If you find anything that looks different, see your doctor or health care provider. Also, ask your doctor to check your skin during regular checkups.

The ABCD rule is a convenient guide to the usual signs of melanoma. Here's what you should be on the lookout for:

• A is for ASYMMETRY: One half of a mole or birthmark does not match the other.
• B is for BORDER: The edges are irregular, ragged, notched, or blurred.
• C is for COLOR: The color is not the same all over, and may have shades of brown or black, sometimes with patches of red, pink, white, or blue.
• D is for DIAMETER: The area is larger than 6 millimeters (about ¼ inch -- the size of a pencil eraser) across, or the area has been growing.

Another very important warning sign of melanoma is that a mole has been growing or changing its shape or color. Some melanomas do not fit the ABCD rule described above, so it is very important to report to your doctor any changes in skin lesions, new skin lesions, any pigmented areas that look different from the rest of your moles, and any sores that don't heal.

Wearing a hat and tightly-woven clothing and avoiding the intense sun from 10 a.m. to 4 p.m. are excellent ways to protect yourself from damaging UV rays and skin cancer. Using sunscreen is also important.

For maximum effectiveness, apply sunscreen 20 to 30 minutes before going outside. Be generous in the amount you use and use a product with a sun protection factor (SPF) of 15 or higher. A palm-full of sunscreen (about 1 ounce) should be enough to cover the arms, legs, neck, and face of an average adult. Less is needed for a child. For best results, most sunscreens need to be reapplied every 2 hours and immediately after swimming or sweating heavily. Remember that sunscreen usually rubs off when you towel yourself dry.

Some people think about sun protection only when they are planning to spend a full day at the beach or pool. But sun exposure happens whenever you're in the sun -- gardening, fishing, walking through the zoo, attending a baseball game, or going to and from your car. Be sure you've got yourself covered every time you go out.

Article updated: 4/22/08