The following report by medical editor Marilyn Brooks first aired June 7, 2005, on Channel 4 Action News at 5 p.m.

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Warnings about skin cancer usually involve exposure to the sun.

But now, researchers say you may also want to check your stress level the next time you slather on sunscreen.

Gary Rasor, a groundskeeper, spent a lot of time in the sun but very little time thinking about its dangers.

Rasor, skin cancer patient: "I didn't think about it at all, did not wear any sunscreen, did not wear a hat or a visor or anything."

Some people get skin cancer once, but not Rasor. Basal cell tumors keep coming back.

The sun may not be the only culprit.

Researchers say a healthy immune system can often kill a basal cell tumor on its own. They know stress and depression weakens the immune system, and they believe that lets tumors grow.

Dr. Janice Glaser, researcher, Ohio State University: "There's really outstanding evidence at this point and time that stress has an effect on the immune system. Both short- and long-term stressors clearly do have a measurable impact."

How much of an impact does it have on skin cancer? Glaser and her husband, Dr. Ronald Glaser, will spend the next three years finding out. They are performing tumor biopsies on more than 300 people, looking for any relationship between the immune response and the patient's report of stress and depression.

Dr. Ronald Glaser: "If you are stressed and if the stress is inhibiting the immune response to the tumor, we should be able to see fewer cells in those tumors taken from stressed individuals."

Researdhers hope the results of their study will help identify those at higher risk for repeated skin cancers, so they can be checked more closely.

Basal cell carcinoma is one of the most common forms of skin cancer in the world. This year, in the United States, there will be more than 1 million new cases.