Showering may be bad for your health, say US scientists, who have shown that dirty shower heads can deliver a face full of harmful bacteria.

美国科学家表示，淋浴可能对健康有害，脏淋浴喷头容易使人接触到有害细菌。

Shower water can contain harmful bacteria

Tests revealed nearly a third of devices harbour significant levels of a bug¹ that causes lung disease.

Levels of Mycobacterium avium（鸟结核分枝杆菌） were 100 times higher than those found in typical household water supplies.

M. avium forms a biofilm（图书显微软片） that clings to the inside of the shower head, reports the National Academy of Science.

In the Proceedings³ journal, the study authors say their findings might explain why there have been more cases of these lung infections in recent years, linked with people tending to take more showers and fewer baths.

Water spurting⁴（溅散） from shower heads can distribute bacteria-filled droplets⁵（小滴，飞沫） that suspend themselves in the air and can easily be inhaled⁶ into the deepest parts of the lungs, say the scientists from the University of Colorado at Boulder⁷.

Potential threat

Lead researcher Professor Norman Pace, said: "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."

While it is rarely a problem for most healthy people, those with weakened immune systems, like the elderly, pregnant women or those who are fighting off other diseases, can be susceptible⁸ to（易感染） infection.

They may develop lung infection with M. avium and experience symptoms including tiredness（疲倦）, a persistent⁹, dry cough, shortness of breath and weakness, and generally feel unwell.

When the researchers swabbed（擦净） and tested 50 shower heads from nine cities in seven different states in the US, including New York City and Denver, they found 30% of the devices posed a potential risk.

Since plastic shower heads appear to "load up" with more bacteria-rich biofilms, metal shower heads may be a good alternative, said Professor Pace.

Showers have also been identified as a route for spreading other infectious diseases（传染病）, including a type of pneumonia¹⁰ called Legionnaires' disease and chest infections with a bacterium² called Pseudomonas aeruginosa.

Hot tubs and spa（矿泉，温泉浴场） pools carry a similar infection risk, according to the Health Protection Agency.