According to a report published in PLOS-One, subjects assigned to take a cold shower for at least 30 seconds at the end of a daily hot shower experienced a 29% reduction in absence from work due to illness. The sick-day-reducing effect of the brief cold shower was comparable to that of regular physical activity. Those who combined cold showering with regular physical activity showed a 54% reduction of illness absence.
The average temperature of the shower water was 10-12 ℃ (50-54 ℉). These results were obtained with just 30 days of cold showering required.
Ninety-one percent of the participants reported a desire to continue the practice and 64% actually did so. Many people also reported a sense of increased vitality.
At the beginning of September 2016 I started taking a straight cold water shower right after getting out of bed. No hot water at the start; just walk right into the cold water. I scrub my skin from head to toe with a wash cloth while under the cold water. I don't know the temperature of the water, but it feels cold when I get in. After what I would estimate as 45-60 seconds, it doesn't feel cold anymore. I think it takes me 2-4 minutes to do the full body scrub. After this I dry myself and start my day. Then I take another brief shower after my morning physical activity, occasionally starting with warm (not hot) water, but on most days, just cold water again.
I feel great after these showers. I have seen and felt an improvement in the moisture of my skin during this time as well.
Humans certainly did not evolve bathing in hot water. People of European and northeast Asian descent had Neanderthal ancestors who inhabited the cold north for at least 300,000 years. They certainly had adaptations to cold exposure.
My cold water bathing experiments will definitely continue.