Physiological Response to Cold: What Happens in the First 5 Minutes of Cold-Water Immersion?

Cold-water exposure is a powerful stressor that challenges the body’s systems—physically, mentally, and emotionally. Just like exercise or hypoxia (low levels of oxygen in tissues), cold exposure disrupts homeostasis and challenges the body to adapt.

During cold exposure, the body must regulate heat production and heat loss to maintain an optimal internal environment, particularly in the brain and vital organs. This post explores what’s happening physiologically in the first five minutes of cold-water immersion. Also, in this post we're focusing on deliberate, controlled cold exposure - always approaching the cold water with safety.

Why does Cold-Water Exposure Triggers a Stress Response?

When the skin detects a sudden drop in temperature, cold receptors in the skin trigger the sympathetic nervous system (fight or flight response). This causes a cascade of physiological effects in the body intended to protect us from danger.

But here’s what’s important to know - with repeated, deliberate exposure, the body adapts, just as it does with exercise. The initial response becomes less intense, and we build tolerance. This process is called habituation.

Factors like age, gender, body composition, and circadian rhythms can influence how our body reacts to cold (Espeland et al., 2022).

What Happens in the First 5 Minutes?

Let’s break down what's happening in our body during cold-water immersion.

0–10 Seconds: Cold Shock Response

The cold shock response is immediate. It’s the moment your system panics. This is the bit that makes you want to jump out.

• Sympathetic nervous system kicks in.

• Rapid increase in heart rate and blood pressure.

• Involuntary gasp reflex and hyperventilation (rapid and sometimes uncontrollable breathing).

• Blood vessels constrict (cutaneous vasoconstriction) to preserve heat in the core.

10–30 Seconds: Breath Control Begins

If you stay in and can stay calm, conscious breathing starts to regulate the stress response.

• Thermoreceptors are still firing, but breathing slows with control.

• Endorphins and norepinephrine begin to release.

• Blood pressure remains elevated, but blood is redirected towards vital organs.

Staying through this phase is when mental resilience is tested and built.

30–60 Seconds: Clarity, Presence, Reset

For many, this is the moment of stillness—the 'reset'.

• Breathing becomes rhythmic.

• The parasympathetic nervous system (rest and digest) begins to rebound.

• Dopamine levels increase (by up to 250% in some studies).

You may feel a wave of calm, clarity, or emotional release. This is the state people often describe as feeling "alive” or “clear.”

(Tipton et al., 2004; Sramek et al., 2000)

1–5 Minutes: Thermogenesis & Vagal Activation

After the initial shock:

• Shivering thermogenesis begins, where small muscle tremors to produce heat.

• Non-shivering thermogenesis may activate, especially in regular cold users, through brown fat (brown adipose tissue).

• Nervous system shifts more fully into parasympathetic mode (rest and digest) .

• Vagus nerve is stimulated: this helps regulate mood, inflammation, and digestion.

• Stress hormones like norepinephrine continue to rise, improving focus, mood, and resilience.

What Influences the Cold Shock Response?

Skin temperature—not core temperature—triggers the cold shock response. This is due to cold receptors in the skin that stimulate the sympathetic nervous system (Lipińska et al., 2024).

Initially, this response can feel overwhelming—like panic or uncontrollable breathing. But with regular, safe exposure, it becomes less intense.

In her book Winter Swimming, Susanna Søberg describes this as habituation: the body's learned ability to reduce overreaction to stress. Over time, heart rate, breathing rate, and blood pressure responses are muted.

This mirrors how we adapt to other hormetic stressors—short, controlled challenges that make us stronger, like strength training or breath-holds.

Why Time and Temperature Matter?

The colder the water, the faster and more intense the cold shock response.

So if the water is very cold, less time is needed to trigger the physiological benefits.

Here’s a general guide based on Tipton’s research (2004):

Temperature	Perception	Physiological Impact
15–20°C	Cool	Mild stimulation. Great for beginners.
10–14°C	Cold	Full cold-shock response. endorphin / dopamine release.
<10°C	Very Cold	Strong sympathetic reaction. Ensure safety with duration to avoid overexposure.

Remember: this isn’t a competition. The goal is nervous system training, not suffering. Shorter, more frequent, controlled exposures are better than pushing for longer durations.

Final Thoughts

Understanding what happens in the first five minutes of cold-water exposure gives us insight to ensure we approach this with safety whilst responding with awareness, not fear.

At Reyt Sauna, we often hear: "I didn’t expect the cold to feel like that.”

That’s the cold shock response. It’s normal, and it’s trainable.

With practice, cold-water immersion becomes less about gritting your teeth and more about leaning into presence. It becomes a tool for regulating the nervous system, boosting resilience, and connecting to the moment.

The breath is your anchor. The cold is the teacher. And the benefits? They ripple far beyond the water.

Ready to try it for yourself? We’re here to guide you—cold, heat, breath, and stillness included.

Castellani, J. W. & Young, A. J., 2016. Human physiological responses to cold exposure: acute responses and acclimatization to prolonged exposure. Autonomic Neuroscience, 196, pp.63–74. Available at: https://doi.org/10.1016/j.autneu.2016.02.009 Wikipedia+6ResearchGate+6ResearchGate+6WikipediaWikipedia+1Wikipedia+1ScienceDirect+12PubMed+12Resear

Lipinska, J, Kowalczuk, M., Lipinski, Ł., Kopec, I. and Margas, M., 2024. Health effects of cold water immersion and swimming and its influence on the human body. Journal of Education, Health and Sport, 52, pp.155–168. Available at: https://doi.org/10.12775/JEHS.2024.52.011 

Tipton, M. J., Eglin, C. M. & Golden, F. .C., 2004. Habituation of the initial responses to cold water immersion in humans: a central or peripheral mechanism? Journal of Physiology, 512(2), pp.621–628. Available at: https://doi.org/10.1111/j.1469-7793.1998.621be.x

Soeberg, S., 2022. Winter Swimming: The Nordic Way Towards a Healthier and Happier Health. Souvenir Press.

Srámek, P., Simecková, M., Janský, L., Savlíková, J. and Vybíral, S., 2000. Human physiological responses to immersion into water of different temperatures. European Journal of Applied Physiology, 81(5), pp.436–442. Available at: https://doi.org/10.1007/s004210050065