Cold showers not only offer their own benefits, but help shield you from the deleterious effects of hot showers. It may sound like a paranoid concern, but experts unanimously agree: hot showers vaporize dangerous amounts of chlorine and other toxical chemicals into the air. This has been acknowledged by the presigious magazine, New Scientist, professor of Water Chemistry, J. Andelman, and the National Academy of Sciences.
“I tell my friends to take quick, cold showers”, said Jullian B. Andelman, Professor of Water Chemistry, University of Pittsburgh, who claimed that the longer and hotter the shower, the more chemicals build up in the air.” – San Jose Mercury News, September 11 1986
“Taking showers is a health risk, according to research presented last week in a meeting of the American Chemical Society. Showers – and to a lesser extent baths – lead to a greater exposure to toxic chemicals contained in water supplies than does drinking water. The chemicals evaporate out of the water and are inhaled. They can also spread through the house and be inhaled by others.” - New Scientist – 18 September 1986, Ian Anderson
“The National Academy of Sciences estimates that 200 to 1,000 people die in the United States each year from cancers caused by ingesting the contaminants in water. The major health threat posed by these pollutants is far more likely to be from their inhalation as air pollutants. The reason that emissions are high is because water droplets dispersed by the shower head have a larger surface-to-value ration than water streaming into the bath.” - Science News – Vol. 130, Janet Raloff
To summarize the above quotes, both the heat and the dispersion of water in a hot shower make carcinogens more likely to vaporize into the air than from a cold shower or bath. Note that while only 200 to 1,000 cancers (in the U.S.) are estimated to be caused directly by these chemicals, cancers usually arise from a combination of multiple offending elements and a weakened immune system. Even if you do not land in this small pool of unlucky victims, hot showers are probably not a healthy habit for overall health.
Also be wary of hot tubs or whirpool baths. Municipal tap water is required to have at least 0.2 ppm of chlorine (enough to kill some fish). Pools typically have between 2.0 and 4.0 ppm chlorine . Hot tubs may be especially dangerous because they could mimic the “hot shower effect” with high chlorine concentrations, generating steam via the water turbulence. This seems like more than ample reason to avoid habitually soaking in hot tubs.
A better alternative to hot showers is combining infrared saunas with cold showers.