A cold shower in the morning is a pretty unpleasant way to start the day. Yet many have been tempted to take up the habit because being immersed in cold water has many purported health benefits, both physical and mental.
Cold showers were first administered for health reasons in the early 19th century when doctors designed them for use on asylum and prison inmates to "cool hot, inflamed brains, and to instill fear to tame impetuous wills".
By the mid-19th century, the Victorians realized that the shower had other uses, namely washing people – and it would be better if the water was warm. So the shower went from being a device used to inflict unpleasantness for an hour and a half to one that was very pleasant and lasted about five minutes.
But what does the evidence show?
A large study from the Netherlands found that people who took a cold shower were less likely than those who took a warm shower to take time off work due to sickness.
A group of over 3,000 people was split into four groups and asked to have a warm shower every day. But one group was asked to end it with 30 seconds of cold water, another with 60 seconds of cold water, another with 90 seconds of cold water.
The control group could merely enjoy a warm shower. The participants were asked to follow this protocol for a month. (Although, 64 percent continued with the cold-water regimen because they liked it so much.)
After a three-month follow-up period, they found that the groups that had cold water had a 29 percent reduction of self-reported sick leave from work. Interestingly, the duration of the cold water did not affect the sickness absence.
The reason a blast of cold water might stop people from getting ill is not clear, but some research suggests it may have something to do with 'boosting' the immune system. A study from Czechia showed that when "athletic young men" were immersed in cold water three times a week for six weeks, it gave a slight boost to their immune system. However, more and larger studies are needed to confirm these findings.
Cold water also appears to activate the sympathetic nervous system, the part of the nervous system that governs the fight-or-flight' response (an automatic physiological reaction to an event that is perceived as dangerous, stressful or frightening).
When this is activated, such as during a cold shower, you get an increase in the hormone noradrenaline. This is what most likely causes the increase in heart rate and blood pressure observed when people are immersed in cold water, and is linked to the suggested health improvements.
Cold water immersion has also been shown to improve circulation. When exposed to cold water, there is decreased blood flow to the skin. When the cold water stops, the body has to warm itself up, so there is an increase in blood flow to the surface of the skin.
Some scientists think that this could improve circulation. A study that looked at cold-water immersion after exercise found that, after four weeks, blood flow to and from muscles had improved.
There is also some evidence that a cold shower can help you lose weight. A study found that cold-water immersion at 14°C increased metabolism by 350 percent. Metabolism is the process by which your body converts what you eat and drink into energy, so a higher metabolism roughly equals more energy burned.
Aside from the physical benefits, cold showers could have mental health benefits too. There is a school of thought that cold water immersion causes increased mental alertness due to the stimulation of the previously mentioned fight-or-flight response. In older adults, cold water applied to the face and neck has been shown to improve brain function.
A cold shower may also help relieve symptoms of depression. A proposed mechanism is that, due to the high density of cold receptors in the skin, a cold shower sends an overwhelming amount of electrical impulses from peripheral nerve endings to the brain, which may have an anti-depressive effect.
There is a fair amount of evidence that cold water immersion or having a cold shower is good for your health – even if the reasons why are still a little unclear.
But before you start turning the cold tap on towards the end of your shower, you should know that there are some risks to a cold shower. Because a sudden gush of cold water shocks the body, it can be dangerous for people with heart disease and could precipitate a heart attack or heart-rhythm irregularities.