Researchers from the University of Colorado used a relatively new technique in microbiology and found potentially dangerous levels of certain bacteria (mycobacteria … similar to tuberculosis) in 30% of the showerheads examined (these were in New York, Chicago and Denver). Some of these bacteria were bleach loving … it actually made them grow faster, so Clorox is not going to help. The bacteria actually hide in slimy biofilms and the most dangerous time is thought to be right when you first turn on the shower. So be sure to turn the shower on for a little bit before you step in. The next factor was that plastic was much better at harboring the mycobacteria than metal, so try to get metal showerheads where possible. We use water saver showerheads which are small, cheap and metal. You can get them at any hardware store. Regardless, if you have a cold, the last thing you want to do is take a long shower with a plastic showerhead. Baths don’t have the same problems so that’s a reasonable option if your immune system is compromised.