Skin cancer is one of the most common forms of the disease but it can often be cured if treated early enough. Ultraviolet (UV) rays from the sun and tanning machines remain the main risk factor but the danger is also influenced by a person's skin type.

A study of 100,000 Scandinavian women showed that high UV ray exposure in their youth was linked to problems later, says biophysicist Ruediger Greinert of the Dermatological Center in Germany.

Physicians recommend regular skin check-ups. "A person should check all over every two months to see if there have been any changes. If anything itches or bleeds for no apparent reason, you should go to a doctor," advises Eckhard Breitbart of the Hamburg-based ADP Working Group on Dermatological Prevention.

"When you check your birthmarks, you should use the so-called ABCD rule," says Breitbart.

The A stands for asymmetry. An at-risk birthmark will not have a regular shape, like the circles and ovals found in so many other skin blemishes.

The B - for borders - is also important. "If the border isn't regular or bleeds outside the original shape, then there is reason for concern," says Breitbart.

The C is for color. A harmless birthmark will tend to be a uniform light brown. Multi-colored birthmarks are a sign of potential danger.

Finally, there is the D for diameter. Breitbart advises keeping a close eye on any birthmark with a diameter of 2 mm or more.

If there is reason to think that a birthmark has changed, it is imperative to have a doctor examine it. An operation at this stage will usually leave nothing more behind than a small scar.

(China Daily via DPA December 16, 2008)