Q: I recently noticed a new mole on my arm. I have had it for about two weeks now. What should I do?

A:Not all changes in the skin are dangerous, but you should see a dermatologist if you notice changes in your skin that last longer than two weeks.

Moles are very common. The average Caucasian has about 20 moles on his or her body. Most moles are harmless, but it is important to know when a mole exhibits signs that suggest it may be a dangerous mole.

A normal mole has a sharp margin, a uniform color, a symmetrical shape, and a smooth outline or contour. Usually, they are less than ¼ inch in size and of a single uniform color.

The ABCD warning signs can often identify dangerous moles.

A: Asymmetry, where one half does not match the other half. (Normally, each half should be a mirror image of the other half.)

B: Border irregularity, where the edges are ragged or blurred, and not sharp

C: Color, in which the pigmentation and color are not uniform throughout

D: Diameter, where the width of the mole is greater than ¼ inch

There is also the ugly duckling sign, in which the mole in question looks or acts differently than all of the other moles on the body. This would include moles that ulcerate, bleed, change shape, change color, or itch.

Other warning signs include any of the following:

• A new growth not previously present on the skin
• Scaliness, oozing, or bleeding from a bump or nodule in the skin
• An area of skin that stays irritated, red, or itchy
• An area of skin that keeps cracking or bleeding
• A colored or dark spot that is getting larger

Skin cancer is almost always curable when found early, but can be deadly if the diagnosis is delayed. Both doctors and patients play important roles in discovering skin cancers early in their course.