Washington ? In what may be the scariest shower news since Alfred Hitchcock’s “Psycho,” a study says showerheads can harbor tiny bacteria that come spraying into your face when you wash.

People with normal immune systems have little to fear, but these microbes could be a concern for folks with cystic fibrosis or AIDS, people who are undergoing cancer treatment or those who have had a recent organ transplant.

Researchers at the University of Colorado tested 45 showers in five states as part of a larger study of the microbiology of air and water in homes, schools and public buildings. They report their shower findings in today’s edition of Proceedings of the National Academy of Sciences.

In general, is it dangerous to take showers? “Probably not, if your immune system is not compromised in some way,” lead author Norman R. Pace says. “But it’s like anything else — there is a risk associated with it.”

The researchers offer suggestions for the wary, such as getting all-metal showerheads, which microbes have a harder time clinging to.

Still, showerheads are full of nooks and crannies, making them hard to clean, the researchers note, and the microbes come back even after treatment with bleach.

People who have filtered showerheads could replace the filter weekly, added co-author Laura K. Baumgartner. And, she said, baths don’t splash microbes into the air as much as showers, which blast them into easily inhaled aerosol form.

The bugs in question are Mycobacterium avium, which have been linked to lung disease in some people.

Studies suggest increases in pulmonary infections in the United States from species like M. avium may be linked to people taking more showers and fewer baths, Pace said.