Researchers from the University of Colorado conducted tests on 45 different shower heads from nine cities in the United States, using genetic testing to reveal bacteria that can’t be detected by the usual method of growing them in a dish.
The type and number of bacteria in shower heads varied from place to place, often corresponding roughly with levels of bacteria in the water supply. However, one type of bacteria, called mycobacteria, appeared in higher numbers inside shower heads. The researchers think these bacteria form a waxy biofilm that’s not easily washed away by water.
The most noteworthy finding was a species called Mycobacterium avium. It’s common, often found in water and soil, and about 20 percent of the swabs gave test results suggesting that Mycobacterium avium could be present. Mycobacterium avium does have the potential to make people ill, although the immune system of a healthy person will almost always keep this germ in check.
“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,” said lead researcher Norman Pace.
Since most people do not stand facing the shower when they first turn it on and attempt to swallow the first water that comes out there is no reason to be alarmed.
“[The study] is nothing to freak out about because most germs don’t hurt you,” says Philip M. Tierno Jr., PhD, the director of clinical microbiology and immunology at New York University Langone Medical Center. People come into contact with 60,000 types or groups of bacteria on a regular basis, says Tierno. “Only one or two percent are pathogenic,” he explains.
If all this talk of bacteria has you worried, before you rush off to bleach your showerhead know that mycobacteria will slowly grow back. When researchers did try treating one shower head with diluted bleach, they ended up with a greater proportion of some (harmless) bacteria in subsequent tests.
Metal showerheads appear to be less likely than plastic showerheads to grow biofilm, according to the researchers. Tierno recommends taking a steel brush and good cleaning solution to wash out metal showerheads or replacing them once a year or more frequently, like they do in hospitals.
If you are still feeling scared that your immune system will not protect you consider taking cold showers since bacteria thrive in warm, moist environments.