Ice baths are trendy. Pro athletes and Instagram celebrities tout them as a post-workout silver bullet, a perfect tool for recovery.

But do they really work?

They can be effective post-exercise, said Professor Rui Li, director of Northeastern University’s exercise science program.

“The most benefits come from reducing the inflammation, especially for athletes or anybody who has done an acute session of exercise, specifically strenuous exercise.” Li said. “Ice bath immersion can definitely reduce and isolate the inflammation induced by local inflammatory factors to the local muscles and body parts.”

But ice baths are not a silver bullet, nor are they appropriate for everyone, she said.

When a person immerses their body (or part of their body) in icy water, she said, it can kick off a number of processes. Temperatures of ice baths are typically around 50-59 degrees Fahrenheit, and immersions should not last longer than 10-15 minutes.

“It's a natural process: When the body is exposed to cold, it's going to turn on a protective mechanism, basically through negative feedback,” Li said. “Basically, our body's blood circulation will be redirected from your body's surface to the internal vital organs and trying to preserve the core body temperature to avoid a fast temperature drop.”

As a result, some people will experience shivering, muscle cramps, racing heartbeats and some challenges to the cardiopulmonary system, she said.

“The individual should be definitely be aware of the risks and be prepared for the stimulation from the cold and the physiological responses that are rendered very quickly,” Li said. “Make sure you have a very healthy, strong autonomic nervous system to regulate your blood pressure, heart rate and also breathing level to the proper levels.”

Also, don’t rely on ice baths for all recovery needs, she said. Supplement them with proper nutrition, especially carbohydrates and protein; stretching; active recovery and relaxation.

“In addition, sleep is a very critical process,” she said. “Getting enough sleeping hours to make sure you allow your body to settle and making those building block blocks, amino acids to your protein recovery.”

The cold plunge-curious can start with higher temperatures and shorter immersions, she said. They can also try just dipping a toe in, so to speak.

“I recommend somebody who has never done an ice bath before to start slow with shorter time of immersion and also with higher temperature,” she said. “They may start from body parts like legs and lower limbs that are more comfortable, and then gradually ease into your core body parts, so over time, your body will be adapting to the temperature.”