Q: I've always had a lot of moles, but I'm not sure if they're dangerous.  How do I know if one could be an early skin cancer?

Any asymmetrical discoloration of the skin, particularly one with irregular borders or color variations, should be examined by a doctor.  A discoloration larger than a pencil eraser, a crusted or bleeding spot that doesn't heal in 4-6 weeks, or any new, unusual marking on the skin, is a strong reason to see a dermatologist. 

Those with fair skin and light-colored eyes, and those of northern European descent are the most likely to get skin cancer, but even dark-skinned people can get it, including African-Americans.  Other risk factors include those with a large number of moles, or a family history of cancer. People in high-risk groups should have regular skin check-ups.

The most common types of skin cancers are basal and squamous cell carcinomas, with more than a million new cases diagnosed in the U.S. annually. 

Basal cell carcinoma usually doesn't spread to organs or lymph nodes.  However, it's locally destructive, so it's prudent to remove it.  Squamous cell carcinoma can move to nodes and metastasize.

Melanoma is the deadliest form of skin cancer, with the highest instance of metastasis. The lower legs in women and the upper back in men are the most common sites for melanoma, although it can occur anywhere.  

About 85 percent of basal and squamous cell carcinomas appear on the head or neck, but they can occur anywhere on the body.  

Most skin cancers are treated in a dermatologist's office.  Mohs surgery is a technique, done under local anesthetic on an outpatient basis, with a high cure rate.  It spares more tissue than other surgical procedures, since only areas that test positive receive additional treatment. It is useful in treating basal and squamous cell carcinomas in high-risk areas of recurrence such as the central face, around the eyes, nose, lips and ears.

The number one factor in the development of skin cancer is sunlight.  The skin is like a camera, holding the "memory" of sun exposure, which accumulates over time.  We receive 80 percent of this exposure by the age of 21.  One blistering sunburn in a lifetime is an especially identifiable risk.

Apply sunscreen with an SPF of 15 or higher, to any exposed skin 30 minutes before going outside.  Wear a broad-brimmed hat and sunglasses that protect from UVA and UVB rays, and avoid being in the sun from 10:00 a.m. to 3:00 p.m.

A tan, including one from a tanning booth, means the skin is trying to protect itself from burning.  There is no such thing as a safe tan.  

 Mark Balle, M.D., is the director of Mohs surgery at Henry Ford Health System.