The beneficial potential of cold-water immersion has been recognized throughout human history, with early references dating back to 1600 before Christ. These beneficial effects of the external application of cold water are also seen in more recent and more systematic approaches. Notably, cold water immersion had significant and positive effects on metabolic and catabolic processes, neurotransmitters and hormones, immune parameters as well as on more global markers of health, such as sick leave and quality of life. Also, cold showers have been proposed to be of use in the treatment of depression and there are anecdotal and uncontrolled reports as well as news coverage on taking cold showers - usually in contrast to warm or hot water - showing positive effects for skin and hair. For example, cold water tightens and constricts the blood flow which gives the skin and hair a healthier glow and decreases transepidermal water loss contributing to better skin hydration, while hot showers can lead to dried out skin. Noteworthy, none of these studies reported negative events related to cold water treatment as well as no negative long-term effects.
Furthermore, a recent study on 3018 healthy participants without any experience of cold showering and which were randomized to a (hot to-) cold shower for 30, 60, 90 seconds or normal (warm) showers for 30 days followed by 60 days of showering cold at their own discretion for the intervention groups - reported that 79% of participants taking cold showers completed the intervention protocol and that taking (hot to-) cold showers reduced sickness absence by 29% in comparison to participants taking normal hot showers (incident rate ratio: 0.71, P = 0.003). Importantly, no related serious adverse events were reported.
Next to these beneficial effects on health and well-being, taking cold showers has a rather neglected, but none the less important effect as taking cold showers substantially reduces individual CO2 emission. On the basis of the CO2 emission of the average electricity mix used in Switzerland (kwH=169g CO2) and the average habit of taking warm showers (Switzerland: 8.7 minutes 6 times per week, with 15 litres/minute of warm water of 35°C), taking warm water showers produces up to 248 kg of CO2 per person and year, which corresponds to a flight from Zurich to Paris and back. This CO2 emission per year significantly increases when the house-hold is run on natural gas (296 kg) or oil (390 kg). By ratifying the Paris Convention, Switzerland has committed itself to reducing greenhouse gas emissions by 50% by 2030 compared with 1990 levels. With the previously calculated example, 15% of per capita CO2 emissions could be saved to meet the 2030 target (25% if the house runs on oil; 19% on natural gas). Considering the urgent need to cut down CO2 emission, this neglected potential could be used to substantially reduce individual CO2 emission, besides achieving beneficial health and well-being effects.
Considering the beneficial individual and environmental effects, investigators set out to replicate the recent study on the effects of taking cold showers on sickness absence, illness days and subjective well-being and to assess both the acceptability of taking cold showers as well as its effects on sickness absence and illness days as well as well-being, sleep quality, skin and hair appearance for a period of 3 months in a population of healthy and volunteering participants.
