Swimmer's itch pegged to parasites.

• Position: Your Life - Parasites in Michigan lake cause of cercarial dermatitis

Lois Verbrugge takes her research personally. When she built a home with her husband on a northern Michigan lake, her scientist's curiosity was piqued by the irritation her skin developed every time she went swimming.

"I started to swim and itched intensely afterward," notes Verbrugge, a professor and senior distinguished research scientist at the University of Michigan Institute of Gerontology, Ann Arbor. "I'm a curious person and started asking questions about what was in the lake."

Verbrugge examined the incidence and risk factors of swimmer's itch, the lay term for cercarial dermatitis, caused by parasites in the water. "Exposure to shallow water and areas with onshore winds are key risks for swimmer's itch." The more days a person is in the lake, the higher his or her chance for having an episode of the painful skin irritation. Like poison ivy or oak, swimmer's itch is a reaction of the skin to an irritant. Larvae of the parasite burrow into the skin of swimmers, causing red, itchy bumps.

When Verbrugge began exploring the epidemiology of swimmer's itch, she found that most existing research looked at ducks and snails, because the parasite that causes the itch has...