The big chill

Athletes and celebrities swear by the therapeutic benefits of ice bathing, which involves briefly immersing one's body in cold water. "Cold" is subjective, but in general ice baths are done at a temperature that feels cold but not freezing. The science around possible health benefits of ice baths is thin. Still, devotees say the practice makes them feel mentally and physically invigorated and reduces muscle soreness.

"Ice baths fall into the category of 'it doesn't hurt to try,'" says Michael Smith, a physical therapist with the Sports Medicine Service at Harvard-affiliated Brigham and Women's Hospital.

Ice baths are not for everyone. Some people have health issues that could worsen when they're exposed to sudden cold temperatures, like heart rhythm abnormalities, high blood pressure, or circulation problems, such as peripheral artery disease or Raynaud's disease, which causes narrowing of the arteries in fingers and toes. Before trying an ice bath, check with your doctor if you have these or any other related conditions.

When you're ready to take the ice plunge, here's how to do it:

Temperature. "What feels cold for one person may not feel cold for another, but an ideal temperature is close to 60° F, which is what most household cold water faucets can emit," says Smith. To make the bath water colder add several trays of ice cubes from your freezer or a bag or two of store-bought crushed ice.

Preparation. Once your tub is filled, immerse yourself as much as possible. Depending on your tub size, this could be up to your waist, mid-chest, or neck.

Duration. To overcome the initial shock, close your eyes and focus on your breathing. Stay immersed as long as tolerable. At first this could be as short as 10 to 30 seconds. "Listen to your body, and don't push yourself if it feels too uncomfortable, or you begin to shiver," says Smith. As you get accustomed to ice baths, you could gradually increase the time to one minute, two minutes, or even up to five minutes. "It's fine to keep them as short as possible if that works for you," says Smith.

There's no set number of weekly ice baths you should take. "It depends on your goals, like whether you want muscle recovery after a workout or need a mental jolt," says Smith. "But for general wellness, two or three days a week is good."

Not ready for ice baths? Try cold showers. While you won't get the full effect of a bath, since you don't immerse your entire body in cold water at once, it's still a good place to begin because you can control the water temperature. After your regular shower, turn the temperature to cold and stand underneath the spray for as long as is comfortable.

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