Cold Therapy - Methods compared
Cold acclimation: what changes over time
Last updated 29 September 2026. How we write this .
With repeated cold, the first thing to change is habituation: the gasp, racing heart and discomfort shrink. Lab studies also show brown fat growing more active within 10 days, with no clear effect on weight.
Start here With repeated cold, the first thing to change is habituation: the gasp, racing heart and discomfort shrink. Lab studies also show brown fat growing more active within 10 days, with no clear effect on weight.
By the end, you will understand What are the different ways a body can adapt to cold? How does the body get used to the shock of cold water? Why do some people not seem to adapt? Where this information comes from Claim-cited evidence. Central research claims on this lesson are linked to specific studies or official guidance.
This lesson links the specific studies and guidance used for its central claims.
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Repeated cold changes the body, but mostly in a quieter way than people expect. The change that shows up first and most reliably is habituation: the gasp, the racing heart and the misery of cold all get smaller. Lab studies show that brown fat, a heat-making tissue, also becomes more active after 10 days to 4 weeks of regular cold, but the extra heat it makes is modest and has not been shown to change body weight.
This lesson follows those changes over days and weeks. The immediate response to cold, from narrowing blood vessels to shivering, is covered in What cold exposure does to your body.
What are the different ways a body can adapt to cold?
US Army researchers John Castellani and Andrew Young, in a 2016 review, describe three patterns of cold adaptation seen in people.
Habituation. The body's response to cold becomes weaker than before. Less gasping, a smaller rise in heart rate, less shivering, and the cold feels less bad. Metabolic adjustment. The body makes more heat, for example by burning more fuel in brown fat. Insulative adjustment. The body gets better at holding on to the heat it has, mainly by clamping down blood flow to the skin harder so the outer layers act as insulation. Which pattern appears depends on how far skin and core temperature fall and how long the exposures last, according to the review. Short, sharp cold dips mostly produce habituation. Long hours in a cool room are what shift metabolism.
How does the body get used to the shock of cold water?
The answer appears to lie in the brain rather than the skin. In a 1998 study at the University of Portsmouth and the Institute of Naval Medicine, Michael Tipton, Clare Eglin and Frank Golden had a habituation group of eight people repeatedly immerse only the left side of their body in stirred water at 10°C, six times for three minutes. A control group of seven had no cold water in between. When both groups then immersed their right side, which had never been trained, the habituation group still showed a smaller jump in heart rate and breathing. The skin on the right side was just as cold in both groups, so the change could not have been in the skin's cold sensors. The authors concluded that the mechanism sits more centrally, in the nervous system.
Part of it may be in the mind. In a 2014 Portsmouth study, Martin Barwood and colleagues gave 12 people seven 7-minute immersions. The first and last were in 15°C water. The five in between were in comfortable water at about 35°C, to get them used to the setting without the cold. Their anxiety before the final cold dip fell, but the gasp, heart rate and breathing rate at the moment of immersion were much the same as the first time. Only the depth of each breath dropped. Feeling calmer about cold water is not the same as having a smaller cold shock.
Why do some people not seem to adapt?
Because the type of exposure matters, and not every routine produces a change. In 1988 Golden and Tipton gave 16 volunteers eight 40-minute immersions in 15°C water. Half rested in the water and half exercised. Both groups developed smaller initial responses to the cold. Only the resting group also developed a smaller metabolic response, meaning they made less extra heat when cold. Exercising during the immersions stopped that adaptation from appearing, and moving in the water masked much of what the resting group had gained.
Cold air can be even less effective. In a 2025 study from the US Army Research Institute of Environmental Medicine, Billie Alba and colleagues had 10 people sit in 8°C air for 2 hours a day for 8 days in a row. Skin temperature, blood flow to the hands and forearms, comfort and finger dexterity were no different on day 8 than on day 1. Eight days of cold air simply did not produce measurable habituation.
Can you build more brown fat?
In lab conditions, yes, to a degree. Brown fat burns energy to make heat instead of storing it. In 2013 Anouk van der Lans and colleagues at Maastricht University had 17 healthy young adults, nine women and eight men, spend 6 hours a day in a room at 15 to 16°C for 10 days in a row. Brown fat activity measured on PET-CT scans rose. The share of extra heat made without shivering, called nonshivering thermogenesis, went up from 10.8% to 17.8% above resting levels during mild cold. By day 10 the volunteers judged the room as warmer, felt more comfortable, and reported 61% less shivering than on day 3.
The study also found what did not change. The volunteers' resting metabolic rate stayed the same, so did the time it took them to start shivering in a cold test, and so did their body weight and body composition. The authors suggested that any extra energy burned may have been balanced by eating more or moving less. There were no differences between the women and men.
A Canadian study led by Denis Blondin went further. Six men wore a suit circulating 10°C water for 2 hours a day, five days a week, for 4 weeks. The volume of active brown fat rose by 45%, from about 66 to 95 ml, and the brown fat's capacity to burn fuel during cold more than doubled. That is a striking rise in percentage terms, but it is a change in a small amount of tissue. Shivering intensity in a cold test did not change.
Does cold acclimation affect blood sugar or weight?
The most surprising result came from people with type 2 diabetes. In 2015 Mark Hanssen and colleagues in Maastricht kept eight people with type 2 diabetes in mild cold at 14 to 15°C over 10 days. Their insulin sensitivity, how well their muscles and other tissues respond to insulin, rose by about 43%. The brown fat explained little of this. Its glucose uptake rose only slightly. Instead, the muscles had moved more GLUT4, the protein that carries glucose into cells, to their surface.
That is a large change in a very small study. Eight people is not enough to know how often it would happen, whether it lasts, or whether it would lower blood sugar over months. It also came from long, carefully controlled cold exposures in a lab, not from short cold showers or ice baths. Nobody should change diabetes care on the strength of it, and the right person to discuss blood sugar with is your GP or diabetes team.
What is still uncertain?
The whole field rests on small numbers. These studies had between 6 and 17 volunteers, mostly young and healthy, and most followed people for 10 days to 4 weeks. None tested whether cold acclimation leads to weight loss, fewer illnesses or a longer life, and the van der Lans study found no change in weight at all. Lab cold rooms and water-perfused suits are also very different from open-water swimming or plunge pools, so the findings do not transfer neatly to everyday cold routines.
Habituation has a safety catch too. A smaller gasp and calmer breathing make the first minutes in cold water less dangerous, but they do nothing to slow the later cooling of muscles or the drift towards hypothermia. Feeling at ease in cold water can make it easier to stay in too long. The lesson Cold shock, blood pressure and who should be careful covers how long habituation lasts and what to do if someone gets into trouble.
This lesson explains research on how the body adapts to repeated cold. It is general education, not medical advice, so talk to your GP before regular cold exposure if you have a heart condition, diabetes, Raynaud's or another long-term illness.
Related in this classroom The studies behind this page Human physiological responses to cold exposure: acute responses and acclimatization to prolonged exposure - Autonomic Neuroscience, 2016Habituation of the initial responses to cold water immersion in humans: a central or peripheral mechanism? - Journal of Physiology, 1998Habituation of the cold shock response may include a significant perceptual component - Aviation, Space, and Environmental Medicine, 2014Human adaptation to repeated cold immersions - Journal of Physiology, 1988Short-term repeated cold air exposure does not impact cold thermoregulatory responses or manual performance in healthy humans - American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2025Cold acclimation recruits human brown fat and increases nonshivering thermogenesis - Journal of Clinical Investigation, 2013Increased brown adipose tissue oxidative capacity in cold-acclimated humans - Journal of Clinical Endocrinology and Metabolism, 2014Short-term cold acclimation improves insulin sensitivity in patients with type 2 diabetes mellitus - Nature Medicine, 2015Sources for this classroom
Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.