Marathon runners appear to face a heightened risk of skin cancer, likely due to more sun exposure or an immune system inhibited by arduous exercise.
Dr. Christina Ambros-Rudolph and colleagues at the Medical University of Graz in Austria studied 210 male and female marathon runners and 210 other people of the same age and sex.
The marathon runners were found to have more atypical moles -- larger than common moles with irregular and poorly defined borders. They also had more so-called liver spots -- harmless lesions, also known as solar lentigines, that are small, flat and brownish.
The number of these moles and liver spots is considered a strong independent indicator of increased risk for developing malignant melanoma.
Writing in the November issue of the journal Archives of Dermatology, the researchers said this was particularly pronounced in the runners who trained at the highest intensity levels.
Only 56% of the runners said they regularly used sunscreen.