Shower heads harbor 100 times the bacteria as regular drinking water, according to new research.
Led by microbiologist Norman Pace, a team of researchers from the University of Colorado, Boulder, analyzed the build-up of microbes in shower heads at 45 sites in the United States.
The result? Significant quantities of bacteria -- nontuberculous mycobacteria (NTM), particularly Mycobacterium avium -- were found in the shower heads, at levels 100 times as high as those found in drinking water.
Their work was published in Proceedings of the National Academy of Sciences.
M. avium is responsible for a type of pulmonary disease in developed countries, cases of which have risen in parallel with the rise in showering, Pace said.
The m. avium bacteria tends to be a problem in municipal water supplies, such as in New York City. Since cities' treatment of the water with chlorine kills most but not all bacteria, the process gives avium a selective advantage.
"For most people, taking a shower is not dangerous, but if you are immune compromised, such as the elderly or pregnant, it could be," he said in a statement.
The disease is more prevalent than TB in developed countries.
His advice? Don't use shower heads made of plastic, which are more hospitable to bacteria than metal ones. And if you see anything crusty on it, toss it in the trash.