Our bodies are built to adapt to environmental stress—and to become stronger in the process. Modern, climate-controlled life effectively removes many of these natural stressors (such as temperature fluctuation), but you can still tap into your body’s adaptive response with frequent cold water exposure (also called hydrotherapy).
A cold shower might sound like a jarring way to start the day, but trust us when we say that it’s worth it. With a bit of practice, you’ll come to cherish this ritual—few others bring such immediate full-body clarity and alertness.
Just as physical exercise helps condition muscles and other associated bodily systems, cold water exposure can help strengthen and improve stress resistance throughout the body. Practiced consistently, cold showers/plunges balance brain chemistry and endocrine health, improve metabolic function and circulation, and even facilitate ideal body composition.
Here’s a more detailed layout of what researchers have to say, in case you still need more evidence before taking the plunge.
Endorphin Release + Mood
Some researchers hypothesize that depression and other mood disorders may be caused by a lack of the physiological stressors that were present throughout millions of years of primate evolution, including “thermal exercise” (i.e. brief shifts in body temperature).
A study designed to test this hypothesis demonstrated that daily cold showers effectively alleviate symptoms of depression. Researchers attribute this antidepressant effect to the activation of the sympathetic nervous system, the release of beta-endorphin and noradrenaline, and the triggering of electrical impulses from cold receptors in the skin (like a sort of subdued electroshock therapy). 
Metabolism + Fat-Burning
Recent research around metabolism and weight loss has revealed that ideal body composition and positive metabolic markers are associated with healthy levels of a type of fat called brown adipose tissue. Obesity and its comorbidities, on the other hand, are associated with high levels of white adipose tissue (and correspondingly lower levels of brown adipose tissue). 
Because cold water activates brown adipose tissue (which the body “burns” in order to produce heat), researchers believe that hydrotherapy can help increase metabolism and facilitate healthier body composition. 
Circulation, Skin Health, + Recovery
Because cold water exposure triggers circulatory response (in order to bring warmer, freshly oxygenated blood to colder areas), regular cold showers help make the circulatory system more efficient. 
Improved circulation leads to other downstream benefits, including lower blood pressure, more radiant skin, and faster recovery from injury. 
The shock of cold water is like a training ground for improving your body’s infection-fighting and disease-resisting potential. Studies have shown that regular cold water exposure stimulates leukoctyes (i.e. white blood cells, which help your body fight infection) and increases levels of endogenous antioxidants). 
In one randomized controlled trial, participants who took daily cold showers reported fewer sick days.  Another study even concluded that cold stress may confer enhanced immunity to various kinds of cancer. 
Let’s not forget one of the most important non-physiological benefits of cold showers: a serious improvement of willpower. The practice itself is simple—all that’s required is the nerve to begin.
Start with your regular hot shower, and turn the water cold at the end. Start with 1 minute of cold water, and build up to 3 minutes (the duration most often used in studies and clinical trials). Some studies also advocate a 5-minute gradual adaptation (i.e. slowly turning the water from hot to cold over the course of 5 minutes) when first beginning a daily cold shower practice.
Avoid hyperventilating or any of the unsustainable breathing techniques sometimes associated with cold water exposure. Instead, just breathe deeply and evenly. It can be helpful to exhale completely right before turning the water cold, in order to combat the shortness of breath that can occur during the initial shock. Practicing Anulom vilom pranayama prior to your cold shower is also a great way to prepare the nervous system.
Consistency is most important, so adopt whatever approach allows you to stick with the practice on an ongoing basis. Commit to a daily cold shower practice for at least a week or two (30 days is ideal, if you’re feeling brave). At the end of your trial period, you can decide whether to discontinue the practice...but by that point, we bet you’ll be a believer.