Q: What are the warning signs of skin cancer?

A: There are several different types of skin cancer, and each can present in a different way.

In general, for non-melanoma skin cancers, be particularly suspicious of any new skin lesions or irritation that persist for longer than a month.

The warning signs for melanoma, the most dangerous form of skin cancer can be summarized with the ABCD rule.

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 include shades of brown or black, or sometimes with patches of pink, red, white, or blue.
D is for DIAMETER: The spot is larger than 6 millimeters across (about 1/4 inch–the size of a pencil eraser), although melanomas can sometimes be smaller than this.

Other warning signs are:

1. A sore that does not heal.
2. Spread of pigment from the border of a spot to surrounding skin.
3. Redness or a new swelling beyond the border.
4. Change in sensation–itchiness, tenderness, or pain.
5. Change in the surface of a mole–scaliness, oozing, bleeding, or the appearance of a bump or nodule.
6. A mole that looks very different from your other moles.

Everyone should have a health care professional perform a full-body skin survey once a year.

Dr. Brent Ridge is the health expert for Martha Stewart Living Omnimedia. You can call and ask him a question live every Tuesday at 2 p.m. Eastern on Sirius Satellite Radio, Channel 112 (1.866.675.6675). You can also follow along as he learns to grow his own food and raise goats on his farm in upstate New York by visiting www.beekman1802.com.

Got a health question for Dr. Brent? E-mail him at drbrent@care2.com.