In ancient times, hot water was a luxury. People had to live near a hot springs in order to enjoy the comfort of a hot bath, so for most of human history people bathed in cold water. But even when the Ancient Greeks developed heating systems for their public baths, they continued bathing in cold water for the health benefits.

The Spartans, hard-asses that they were, felt hot water was for the weak and unmanly. When they did take baths (which was, like, once a year) they used only cold water because they thought it tempered the body and made it vigorous for Bottom kicking.

Benefits of Cold Water Showers.
While doctors may no longer instruct their patients to take a cold bath and call them in the morning, a shot of cold water can still impart real health benefits:

Improves circulation. Good blood circulation is vital for overall cardiovascular health. Healthy blood circulation also speeds up recovery time from strenuous exercises and work. Alternating between hot and cold water while you shower is an easy way to improve your circulation. Cold water causes your blood to move to your organs to keep them warm. Warm water reverses the effect by causing the blood to move towards the surface of the skin. Cold shower proponents argue that stimulating the circulatory system in this way keeps them healthier and younger looking than their hot water-loving counterparts.
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Relieves depression. Lots of great men from history suffered bouts of depression. Henry David Thoreau is one such man. But perhaps Thoreau’s baths in chilly Walden Pond helped keep his black dog at bay. Research at the Department of Radiation Oncology at Virginia Commonwealth University School of Medicine indicates that short cold showers may stimulate the brain’s “blue spot”- the brain’s primary source of noradrenaline — a chemical that could help mitigate depression. I guess a bout of the blues isn’t so bad after all.

Keeps skin and hair healthy.
Hot water dries out skin and hair. If you want to avoid an irritating itch and ashy elbows, turn down the temperature of your showers. Also, cold water can make your manly mane look shinier and your skin look healthier by closing up your cuticles and pores.

Strengthens immunity. According to a study done in 1993 by the Thrombosis Research Institute in England, individuals who took daily cold showers saw an increase in the number of virus fighting white blood cells compared to individuals who took hot showers. Researchers believe that the increased metabolic rate, which results from the body’s attempt to warm itself up, activates the immune system and releases more white blood cells in response.

Increases testosterone. During the 19th century, many doctors and ministers recommended that young men take baths in cold water to reduce the sin of “self-pollution,” i.e. whacking off. Cold water was thought to extinguish a man’s flaming carnal desires. There was even a ghastly device invented on this principle.

How wrong they were! The same study by the Thrombosis Research Institute cited above showed that cold water showers actually increase testosterone production in men. Increased testosterone levels not only boost a man’s libido, but also his overall strength and energy level. If you’re looking to increase your testosterone, instead of juicing up like Mark McGwire, hop into a cold shower.

Increases fertility. Trying to become a dad? Cold showers are good for your little swimmers. Your testes aren’t meant to get too hot; that’s why they hang outside your body. Sperm counts decrease when the temperature of a man’s testes increases. Experiments done in the 1950s showed that hot baths were an effective contraceptive. Men who took a 30 minute hot bath every other day for 3 weeks were infertile for the next six months. More recently, the University of California at San Francisco did a study with men who were exposed to 30 minutes of “wet heat” (hot baths and such) a week. When the men cut this exposure out, their sperm count went up by 491%, and their sperm’s motility improved as well. While switching from a hot to cold shower may not have as dramatic an effect, if you’re trying to create some progeny, it surely won’t hurt.

Increases energy and well-being. Every time I end a shower with cold water, I leave feeling invigorated and energized. Your heart starts pumping, and the rush of blood through your body helps shake off the lethargy of the previous night’s sleep. For me, the spike in energy lasts several hours. It’s almost like drinking a can of Diet Mountain Dew, minus the aspartame. And while it hasn’t been studied, many people swear that cold showers are a surefire stress reducer. I’m a believer.

Getting Started with Cold Water Showers
If you’ve spent most of your life taking hot showers, suddenly turning the dial in the other direction can be a big shock to the system. When I decided to get started again with them, my heart almost jumped out of my chest, and I nearly passed out from hyperventilating when the cold water hit my body. Too much, too soon.

My suggestion (based on personal experience) is to gradually decrease the temp of the water so your body can adjust.

Which reminds me, some people with certain conditions should avoid cold showers because of the shock to the body’s system. If you have the following conditions, you’ll have to harness your inner 007 another way:
Heart disease. If my normal, healthy heart felt like it was about to explode, imagine how a diseased heart will feel.
High blood pressure. The contraction in your blood vessels caused by cold water could cause a stroke. Apparently.
Overheated or feverish. Your blood vessels need to dilate in order to release heat. Cold water causes them to constrict.