Showers may be far dirtier than we think

A study out of the University of Colorado shows that biofilms clinging to the innards of bathroom showerheads can harbor up to 100 times the levels of pathogens found in city water.

Elizabeth Armstrong Moore
Elizabeth Armstrong Moore is based in Portland, Oregon, and has written for Wired, The Christian Science Monitor, and public radio. Her semi-obscure hobbies include climbing, billiards, board games that take up a lot of space, and piano.
Elizabeth Armstrong Moore
2 min read

As if we didn't already have enough germs and toxins to deal with in our home environments (the lead in our paint; flame retardants in our furniture; indoor air quality and even the resulting air purifiers; to name a few), we now get to fret over another perpetrator: the showerhead.

Researchers at the University of Colorado at Boulder have just published a study in the Proceedings of the National Academy of Sciences finding that about 30 percent of the showerheads in nine cities (including New York, Chicago, and Denver) carry "significant" levels of Mycobacterium avium, a pathogen that is linked to pulmonary disease.

Biofilms clinging to the insides of showerheads can harbor up to 100 times the levels of pathogens found in background municipal water, according to a new University of Colorado study. Glenn Asakawa, University of Colorado

Moreover, the M. avium pathogen was often clumped together with other pathogens in a slimy biofilm that clings to the insides of showerheads at more than 100 times the levels found in municipal water.

"If you are getting a face full of water when you first turn your shower on, that means you are probably getting a particularly high load of Mycobacterium avium, which may not be too healthy," says lead author Norman Pace, a distinguished professor in the Molecular, Cellular and Developmental Biology department who won the nation's highest award in microbiology in 2001, as well as a MacArthur Foundation "genius grant" for his work.

In addition, research at Denver's National Jewish Hospital suggests that the increase in pulmonary infections in the U.S. in recent decades may be the result of people taking more showers and fewer baths, Pace says. Even those who are careful never to swallow the water spurting from showerheads can inhale the pathogens, which are distributed from water droplets into the air.

Cigarette smoke is the most common cause of pulmonary disease, according to the National Heart, Lung, and Blood Institute, but general air quality also plays a role. Some 7.6 million U.S. adults were diagnosed with chronic bronchitis (a type of pulmonary disease) in 2007, according to the Centers for Disease Control and Prevention.

Symptoms of pulmonary disease that has been caused by M. avium can include weakness, shortness of breath, and a persistent, dry cough; obviously the immune-compromised, such as pregnant women and the elderly, are more prone to experience such symptoms, says Pace.

Previous studies by Pace and his colleagues have found massive enrichments of M. avium in the soap scum commonly found in places such as the surface of vinyl shower curtains. In 2006, Pace and colleague Mark Hernandez found that high levels of M. Avium in indoor pool environments led to pneumonia-like pulmonary conditions in workers known as "lifeguard lung."

Pace says that people with strong immune systems are probably in very little danger of being compromised, but he suggests that there is a higher risk associated with plastic showerheads than metal ones. And if all that isn't enough to swallow, water monitoring in the U.S., according to Pace, is "frankly archaic."