Cleanliness may be a pleasant side effect, but the key lies in the water temperature.
The study's author, Nikolai Shevchuk, believes the biological explanation revolves around a part of the brainstem known, appropriately enough, as the locus ceruleus, or "blue spot."
Shevchuk, who formulated the theory while working in the Department of Radiation Oncology at Virginia Commonwealth University School of Medicine, told Discovery News that short, cold showers may stimulate the blue spot, which is the brain's primary source of noradrenaline -- a chemical that could help mediate depression.
"The possible antidepressant effect may also have to do with the mild electroshock delivered to the brain by a cold shower, because of the unusually high density of cold receptors in the skin," he added, explaining that these nerve endings are 3-10 times higher in density than those registering warmth.
Shevchuk proposes that depression may be caused by two factors. The first is a genetic makeup that predisposes an individual to the disorder. Prior research has documented that depression can run in families, but since some sufferers report no prior family history and many people develop depression later in life, genes don't appear to explain all cases.
He suspects a lifestyle lacking sufficient physiological stress, such as brief changes in body temperature, may also be a contributing factor.
A paper on the theories has been accepted for publication in the journal Medical Hypotheses
Shevchuk said that, throughout the evolution of mammals and primates, individuals got plenty of exercise and were exposed to frequent changes in body temperature, such as when forced to swim in cold water while hunting or when chasing prey in very hot weather.
He links these temperature jolts to the phenomenon of homeopathy, whereby small doses of something harmful may actually promote healing by stimulating the body's repair and recovery systems. Electric shock and deep brain stimulation treatments operate on a somewhat similar principal, only with frightening potential side effects, such as memory loss and cognitive impairment.
Cold showers could also have adverse effects, particularly for heart patients and other already at-risk patients, so Shevchuk advises those who wish to try out the treatment to check with their doctors first. The recommended approach is to take a cold shower -- around 68 degrees -- for 2 to 3 minutes once or twice daily, preceded by a five-minute gradual adaptation to the temperature.
The approach could explain the discovery by psychiatrist Thomas Wehr of the National Institute of Mental Health that people who chronically suffer from depression in the summer benefit from frequent cold showers. Traditional Chinese medicine has also prescribed cold-water swims or baths as mood-lifters.