The American public is regularly bombarded with frightening health warnings about everyday items. Salt causes heart disease; coffee and french fries can kill. And now, researchers have identified the latest health risk — showers.

Just when you thought it was safe to go back in the water... But, seriously, is this just another medical scare story or is cleanliness really next to a case of liver cancer?

"Concentrations of THMs were about 1,000 times lower in blood than in tap water, but after the showers, median levels in blood increased by a factor of four"...

Researchers found that chemicals called trihalomethanes, or THMs, are created when chlorine used to disinfect water interacts with organic matter found in raw water. Scientists have long known that THMs can cause cancer and contribute to reproductive problems such as miscarriage. The news from this study, however, is that when a person showers, THMs enter their bloodstream in much higher amounts than was previously thought.

The study, conducted at the University of North Carolina at Chapel Hill School of Public Health, looked at fifty women in Georgia and Texas. It compared the distribution of THMs in the women's blood with that found in the tap water in their houses and found that THM levels shot up after the women took a shower. "Concentrations of THMs were about 1,000 times lower in blood than in tap water, but after the showers, median levels in blood increased by a factor of four," said environmental engineer Amy Miles, a co-author of the study. "This showed THMs were getting into the blood as a result of water use."

So is chlorination dangerous? Should we go back to washing in streams and lakes?

Not at all, according to Miles. "Chlorination of tap water was one of the most important improvements made in public health, and it saves countless lives each year by reducing risk from bacterial contamination," Miles said. "Water-borne diseases used to be a major cause of death and illness, and they still are in some parts of the world without chlorination."

TheDoctor's oncology expert, Robert Lerner, M.D., Professor of Medicine and Professor of Pathology at New York Medical College and chief of Hematology at Westchester Medical Center, agreed that the study raises an important issue, but he does not recommend that anyone start washing with Perrier just yet. "There is a considerable safety margin," Lerner said, "According to one published study, the amount of THMs that reach the liver even in a worst-case exposure scenario was at least 6,000 times lower than the levels which cause liver cancer in laboratory animals. Based on this, there does not seem to be much risk for humans from household exposure."

"Still," Dr. Lerner continued, "the UNC study provides clear evidence that there is a transfer of trihalomethanes from shower water into the blood. The authors rightly point out that this should be studied, and in fact it is being studied."

Reviewed by Robert G. Lerner, M.D.