What happens to your body in a polar plunge

It's a frigid winter day and yet you're at the beach. The air temperature is 20 degrees, the water is only slightly warmer and you've just stripped down to your bathing suit as the countdown begins. 

You hear "3-2-1," and then, an air horn sounds, ushering you and the crowd of "polar bears" to charge into the ocean. There's splashing and screaming and laughter all around you, but what's going on inside your body as you hit that water?

There's a thing called the "'cold shock response,'" said Dr. Sanjey Gupta, vice chairman of emergency medicine at Long Island Jewish Medical Center and an expert in wilderness and environmental medicine.

Within seconds, your skin is the first organ to react to the extreme conditions. "It has a lot of cold receptors and  ... when your skin hits that water, blood vessels constrict right away," Gupta said. He explained that this is your body's attempt to preserve warm blood for your core, "vital" organs including your heart and your brain.

As blood rushes to your core and away from your extremities, it's not just your skin that will get cold, but also anything beneath it including your muscles. At the same time, this surge in blood flow to your heart will also raise your heart rate and your blood pressure.

Of course, you'll also get a surge of adrenaline as the sudden change in your environment activates your "fight or flight" response," Gupta said. And another almost instant reaction you'll notice is that your respiratory rate rises.

You may even feel like you're hyperventilating as "cold water gives your body the strong desire to start breathing faster," Gupta said.

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And you might also start to feel like your muscles are "freezing" up.

"There’s a consequence to breathing this fast and blood pulling away from your muscles," Gupta said. You may start to feel weak, the pH levels of your blood can be altered and your calcium levels may temporarily decrease.

"There have been people who drown in really shallow water, because they hit the cold water and their muscles seize up and they can’t coordinate," he added.

Assuming you ease yourself into the water, some of these effects may take several minutes to set in, but if you cannonball or dive in head first, that will accelerate your body's response, Gupta said. And the temperature of the water is also a factor, meaning the colder it is the quicker your body will react.

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But it is possible to train your body to better handle these conditions. "You can reduce these effects through exposure," Gupta said. For example, practicing jumping into a cold shower can be one way to prepare your body for an upcoming polar plunge, he added.

And even if the air and the water are around the same temperature, you lose heat quicker when you're in the water, so don't stay in there too long, Gupta said. And once you are back on land, it's important to dry off right away and change into warm, insulating clothes or else you will continue to lose heat.

Another tip: If you are going to jump in, hold your breath. It's normal for your body to want to involuntarily gasp in reaction to the cold water and if this happens when you're below the surface you could breath in some of the water, causing you to aspirate, Gupta explained.

As for any concerns about frostbite, Gupta said that's unlikely because you would need freezing conditions, but you could be prone to nonfreezing cold injuries such as frost nip.

But assuming you exercise good judgment and don't have any pre-existing heart conditions, Gupta said you should fare just fine. Those who have been diagnosed with any form of heart disease, arrhythmias or high blood pressure, he said, should probably refrain from this activity.

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"Play it safe," Gupta said.

Oh, and if you think imbibing in alcohol beforehand will give you the liquid courage to charge into the chilly waters, don't do it.

Alcohol dilates your blood vessels, which means "you can lose the ability to maintain heat in your core, so you can get colder faster," Gupta said. And being under the influence "could also interfere with muscle coordination, which is already going to be challenged with cold water emersion."

And he offered one last sound piece of advice: "Do this with a buddy to make sure you both get out."