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Cold Water’s Effect on the Nervous System

Updated: Aug 16, 2023

A girl cold plunges in a river during winter

Did you know that cold water can activate your sympathetic nervous system and your parasympathetic nervous system? In other words, when you immerse yourself into cold water, your fight-or-flight or stress response kicks on. But when you put cold water on your face, your body responds in the opposite way, by relaxing. So when you do both at the same time, both responses turn on simultaneously, causing conflict in the cold!

Why does this matter? When you activate your stress and relaxation responses through deliberate cold exposure, you train your autonomic nervous system to find balance, which can balance your body’s functions and equip you to better deal with stressors in daily life.

So, what is our autonomic nervous system?

The autonomic nervous system is the nervous system in our body that works automatically, without us having to think about it. There are two main parts of it as mentioned above: the sympathetic response, otherwise known as fight-or-flight (or freeze), and its opposite, the parasympathetic response, otherwise known as rest and digest.

Sympathetic Response

Imagine you are walking down the street on a warm, calm day. You hear birds chirping, the sky is blue, and the sun is gently caressing your skin. Then all of a sudden, the neighbor’s bulldog breaks free from its chain and starts to chase after you. Your heart begins to race, blood pressure increases, pupils dilate, and adrenaline floods your body. You begin to run, faster than you thought you had in you. You gotta get out of there!

This is an example of your sympathetic nervous system kicking into gear. It’s what controls the fight-or-flight responses, and always appears as a response to stress. Literally, it prepares the body to move strenuously – to protect you, to help you survive the stressor.

During the sympathetic nervous response:

  • Heart pumps more blood per minute.

  • Muscles receive more oxygenated, nutrient-rich blood.

  • Lungs bring in more oxygen from the atmosphere and eliminate more carbon dioxide from the body.

  • The pupils dilate and the lens adapts for distance vision.

Parasympathetic Response

Now, imagine yourself running up the steps to your house. As you hear the dog approaching from behind, you fumble with your keys from your pocket. Then you jam the key into the keyhole, yank on the doorknob, and let yourself inside. You slam the door, your heart still pounding. You flop onto the couch, exhausted.

Eventually, your heart rate returns to normal, breathing slows, and you relax. Now that you are safe, your parasympathetic nervous system responds.

The parasympathetic system controls basic bodily functions, such as digestion. When you’re relaxed, normal functions can occur regularly and the body repairs itself.

Some manifestations of the parasympathetic response:

  • Heart rate decreases, which helps to conserve energy at rest.

  • Saliva increases for more ease swallowing food.

  • Ingested food is processed and nutrients are absorbed.

  • Bladder contracts and relaxes, which allows urination.

  • Pupils contract and the lens adapts for near vision.

The cooperation of the sympathetic and parasympathetic systems is necessary to maintain mind-body balance. If we are too often stressed (sympathetic), we can develop chronic stress or other illnesses. If we are too often in our parasympathetic mode, we may have a stress-free, relatively boring life where no growth can occur. The right amount of good stress is healthy and promotes progress and change. With a healthy balance between the two systems, we are able to function effectively in daily life.

Cold water's effects on the nervous system

What are cold water's effects on the nervous system? Think of the first time you jumped into a body of cold water. You may have begun to hyperventilate, or your muscles contracted, or your heart rate skyrocketed and you began to panic. That was your fight-or-flight response in action.

Your body reads the extreme cold as a stressor or sign of danger (even as you do it safely), so the sympathetic nervous system turns on to protect your vital organs. Hormones and neurotransmitters release to prepare your body for survival.

But when your face is wet with cold water (70°F or below), the trigeminal facial nerves detect the cold, transmit the information to the brain and stimulate the vagus nerve. Blood flows toward the core to keep your vital organs warm and heart rate slows 10-30%. This reaction is something that mammals share, and it’s called the diving response or reflex. It functions to preserve oxygen stores during times of water immersion, to protect from drowning. As the heart no longer needs to pump blood to the extremities, blood pressure lowers, relaxing you.

With both systems activated simultaneously from the cold water, there is a physiological conflict in the system – stress response and relaxation! It may explain why you initially want to hyperventilate upon getting into the cold water, and then you gradually sink into a state of calm.

Stress in Daily Life vs. Stress from Deliberate Cold Exposure

Essentially, through immersing our bodies in cold water, we are training ourselves to raise our stress threshold. Stressing the body slightly in a controlled environment is so good for us – it teaches us to better handle stress that is not in our control. And when we put our face in cold water, we can stimulate our vagus nerve which can also relax us.

To be clear, dunking your head under the water is not necessary to receive benefits from cold exposure — find what works for you. Simply getting into uncomfortable (but safe) temperatures can help us learn how to calm ourselves down in a difficult, painful moment, especially as we utilize our breath, meditation, or mindfulness. Then we’ll be more prepared to tackle stress in real life.

Now...who’s ready to plunge?


[Rangan Chatterjee]. (2023, Jan 4). What Happens After 30 Days of COLD SHOWERS? - This Will SHOCK YOU! | Dr. Susanna Søberg [Video]. YouTube.

“Vagus Nerve: Gastroparesis, Vagus Nerve Stimulation & Syncope.” Cleveland Clinic, Accessed 28 June 2023.

[Dhru Purohit]. (2023, March 16). The INSANE BENEFITS Of Heat & Cold Therapy After 30 Days (TRY THIS & SEE RESULTS)|Dr. Susanna Søberg [Video]. YouTube.

Severinsen, Stig. “The Diving Reflex.” Breatheology, 14 Sept. 2022,

Søberg, S. (2022). Winter Swimming (E., DeNoma, Trans.) Maclehose Press.

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