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The Science Behind Cold Plunge

Man getting out of an ice hole

The Science Behind Cold Plunge

I’m sure by now you’ve come across videos of celebrities and influencers slowly lowering themselves into ice bath tubs.

You watch the person tense up and their eyes widen when the icy shock first hits them. They proceed to lower themselves in until they’re submerged to their neck. After a while their breathing becomes controlled, they appear to relax, and they almost seem to be enjoying it. They eventually climb out, and despite their shivering, they’ve got a huge smile on their face. They’ve just taken the cold plunge.

If you’ve never tried it though you may be forgiven for wondering how anyone could do that voluntarily, let alone enjoy it.

But advocates of cold plunge say it’s fun and comes with a host of science-backed health benefits. In this piece, I’ll break down the emerging trend of cold plunge, the science behind it, and the reasons why you may want to consider taking the cold plunge too.

What is Cold Plunge?

Cold plunge, ice bathing, cold hydrotherapy, or whatever you want to call it, are all forms of cold water immersion (CWI). CWI is exactly what it sounds like – it’s the practice of submerging part or all of your body in cold waters of 15°C (59°F) or less.

You may have unwittingly done some CWI if you’ve ever swum in a cold body of water such as the sea or a lake!

But despite its recent popularity, it’s by no means a new idea. It’s an old practice that has been around for millennia, historically popular with athletes, soldiers, and people with chronic injuries.

But thanks to cold therapy advocates such as Wim Hoff and mounting scientific data about the health benefits, CWI has seen a renaissance of popularity. However, most people do not have access to a lake and would rather enjoy the health benefits of CWI from the comfort of their homes. Modern times demand modern solutions after all.

Enter the ice bathtub. Simply fill a tub with water and then add ice to reach your desired temperature. If you want to be as efficient as possible, you can even get electric tubs that cool the water to the desired temperature. Think of a hot tub, but backward!

What Are The Benefits of Cold Water Immersion?

So you understand about CWI and ice bathtubs. But you’re still sceptical about the actual health benefits of subjecting yourself to an icy plunge. Well lucky for us there’s lots of emerging scientific evidence about the health effects of cold therapy and CWI.

The reason that CWI is thought to bring about positive health changes is that it functions as a form of hormesis. Hormesis is the field of science that studies how small doses of potentially harmful substances, hormetic stressors, can result in positive health benefits. Good hormetic stressors provide enough stress to force healthy adaptation (0), but not enough stress to harm you. AKA it hits the sweet spot of stress. This hormetic stress is the same stress that’s responsible for the health response with exercise, intermittent fasting, and infrared sauna.

Let’s take a look at what the scientific research says about the hormetic benefits of CWI:

Increased Fat Burning

It’s thought that cold exposure promotes the production of brown fat (1). Despite what you may think about fat, this kind of fat is very good for us.

Brown fat is a type of body fat that turns on when we become cold. Its purpose is to help maintain your body temperature. The magic of brown fat is that it contains many more mitochondria and has a richer blood (oxygen) supply than white fat. This combination of more mitochondria and more oxygen makes brown fat much better at burning calories than white fat!

Immune Support

Oxidants are oxygen molecules that damage cells and DNA. Anti-oxidants are molecules which neutralise these damaging oxidants. There is evidence to suggest that CWI can boost immune strength by increasing antioxidants, with one study demonstrating how cold water swimmers have increased blood antioxidants(2).

Pain And Fatigue Management

Let’s say you’ve just crushed a great back workout. Do you find you suffer from excessive post-workout soreness the next day? Well, this is probably the most common reason for people taking the cold plunge.

Post-workout CWI has been shown to significantly reduce post-workout soreness and fatigue(3). The theory is that cold water causes the blood vessels to constrict, which reduces the amount of blood flow to the area. This decrease in blood flow leads to a decrease in the amount of inflammation and a reduction in pain.

Another study found cold therapy gave a short-term reduction of chronic pain in people with inflammatory conditions(4). It was thought the reduction in pain was from reduced sensitivity of nerves.

Lowers Heart Rate And Reduces Variability

The vagus nerve is an important part of the autonomic nervous system which controls many of the body’s automatic “rest and digest” functions. One study found that CWI can help to reduce heart rate and stabilise heart rate variability via stimulation of the vagus nerve.

These two factors, low heart rate and stable heart rate variability, are important for long-term heart health(5).

How To Get Started With Cold Water Immersion?

So I’ve convinced you to give CWI a try. But how exactly does someone start to take the cold plunge?

Well, I do not recommend you jump straight into an ice bath with no prior experience. Instead, I would recommend beginning with a daily cold shower, and gradually lowering the temperature over the next few weeks.

This will do three things:

  1. Build up your tolerance for cold
  2. Teach you about how your body responds to cold water therapy so you can plunge safely
  3. Will expose you to many of the benefits of cold immersion with a lot less of the discomfort.

Once you’re comfortable in the shower and want to take it to the next level, then grab an ice bath tub and get ready for the real plunge. Start with very short periods and gradually build up over time. Unless trained and experienced, limit your sessions to 10 minutes. And always observe the 4 stages of cold(6).


So if you’re looking for a great way to improve your health, reduce post-workout symptoms, and build your immune system, consider giving an at-home cold plunge a try! Remember to start off slow and build up. I’m sure you’ll be an ice bath master in no time. Stay safe and enjoy the plunge!

About The Author
Dr Michael Njunge is a practising MD with a passion for health and biohacking. On his blog,, he shares tactics and resources to help people achieve feel-good high-performance healthy living.
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