One of the cleanest places in your home may in fact be one of the dirtiest, according to new research that suggests your showerhead is a breeding ground for bacteria.

According to researchers at the University of Colorado at Boulder, showerheads are a sanctuary for tiny microbes that are released when the water is turned on, msnbc.com reported. Bathers often inhale the tiny spores, which have been linked to lung disease.

“Showerheads provide a dark, wet, and warm environment for microbes to grow,” researchers said in a study first published in the September 14 online edition of the journal Proceedings of the National Academy of Sciences.

The study is based on samples taken from 45 showerheads in homes, apartment buildings and public spaces in New York, Illinois, Colorado, Tennessee and North Dakota. Comparing the water before and after it passed through the showerheads, researchers found that one in five samples contained “significant levels” of Mycobacterium avium, a bacteria linked to lung disease, according to lead researcher Norman Pace.

How much bacteria was there? The pathogens coated the inside of showerheads at more than 100 times the level found in public water supplies where the water came from, researchers said. The trickle-down effect for the average bather is this: Bacteria and other pathogens build up in a biofilm coating inside your showerhead, spraying out when you turn on the water. More often than not, you unwittingly inhale the spores into the deepest part of your lungs.

Can the bacteria harm you? Researchers said m. avium can cause respiratory symptoms like tuberculosis but they said the bacteria levels are not harmful to healthy individuals. Individuals with weakened immune systems can become compromised.

To avoid contact with the bacteria, researchers suggested letting the shower run for 30 seconds while the microbes spray out. Since cleaning showerheads sufficiently is so difficult (think: nooks and crannies), Pace recommended changing your showerhead frequently. Chlorine-bleach products may be effective in removing some bacteria, but not mycobacteria. Pace recommended an all-metal showerhead since microbes easily leach onto plastic.

“It’s like anything,” he said. “There is a risk associated with it.”