When the American team for the 1998 Winter Olympics did a field exercise test, 23 percent of all athletes showed exercise-induced bronchoconstriction, which means a fall of at least 10 percent in FEV1, the amount of air you can push out in the first second of a hard exhale. Among the cross-country skiers it was 50 percent (Carlsen, 2012). Breathing cold air during exercise puts a load on the airways that skiers feel most, but everyone who trains outside between October and March shares a smaller version of it.
Why cold air makes the airways react
Air has to arrive in the lungs warm and nearly saturated with water vapour. When you exercise hard, you move large volumes of air, much of it through the mouth, and the lining of your airways has to do the warming and humidifying. In cold, dry air that costs heat and water.
Reviews describe two main explanations. In the thermal explanation, the cooling itself triggers nerve reflexes that tighten the muscle around the bronchi. In the osmotic explanation, water loss makes the fluid lining the airways saltier, and cells respond by releasing mediators such as histamine that also cause the muscle to contract (Carlsen, 2012; Ora et al., 2024). Carlsen adds a hypothesis: years of repeated, long, high-ventilation sessions in the cold may irritate the lining and raise its reactivity. That part is a proposal, not a proven chain.
What the numbers look like in athletes
Prevalence figures depend heavily on who was tested and how. In Carlsen's review, a clinical asthma diagnosis was present in 42 percent of Swedish cross-country skiers but 12 percent of young Norwegian skiers. Airway hyperresponsiveness, measured with the drug methacholine, showed 43 versus 14 percent. In one study cited there, hyperresponsiveness was highest after the coldest part of the year.
A 2024 narrative review (Ora et al.) puts the prevalence of respiratory conditions in athletes at 20 to 70 percent depending on the sport. That is a wide range, and it is a good reminder that single percentages from single studies should not be read as a rule for you.
What heat and moisture exchangers did in trials
A heat and moisture exchanger (HME) is a device worn over the mouth that catches part of the warmth and moisture of your exhaled breath and hands it back on the next inhalation. Three small crossover trials, in which every person tried every condition, are worth knowing.
In 1992, Nisar and colleagues tested a prototype on four healthy people and on asthmatic volunteers. With the mask, inspired air measured 19.1 °C when the surrounding air was minus 13 °C. In seven people with asthma exercising in that cold air, the median fall in FEV1 was 10 percent with the mask and 22 percent with a dummy mask.
In 2020, Jackson and colleagues had 26 adults with asthma cycle at 8 °C and 24 percent humidity, six minutes at 80 percent of peak power. Eleven had no bronchoconstriction and were removed from the analysis. In the rest, FEV1 fell by 6 percent (SD 7) with the HME, 11 percent (SD 11) with a sham mask and 13 percent (SD 9) with no mask.
In 2022, Stenfors and colleagues studied 23 healthy, trained adults running on a treadmill at about minus 15 °C. Nobody reached the 10 percent threshold, yet the small FEV1 drop seen without the device was prevented with it. CC16, a protein released by airway cells that researchers use as a marker of stress on the airway lining, rose 27 percent with the HME and 121 percent without. Participants also reported less irritation in the upper and lower airways.
The honest limit
These are short experiments with 15 to 26 analysed people, and they measure a few minutes of exercise, not a winter of training. In the 2020 trial the sham mask also seemed to help a little, and the authors say it may not have been fully inert. Cough over the following 24 hours did not differ between conditions.
The 2022 trial found the same rise in inflammatory signals (interleukin 6, 8 and 10) with and without the device, and breathlessness did not change. In the 4-minute maximal time trial, distance was slightly shorter with the device, 918 versus 931 metres. Whether any of this changes long-term airway health is not answered by these studies.
One more gap: in the sources I checked, I found no controlled trial that isolates nasal-only breathing in cold air. The nose does warm and humidify air, as described in our articles on mouth breathing and on nasal breathing for athletes, but at high intensity the mouth takes over, so a cold-air benefit of nasal breathing remains a plausible idea rather than a measured result.
How to actually use it
Start easy. Ora and colleagues list a gradual warm-up among the non-drug measures for exercise-related airway symptoms. Ten relaxed minutes before the hard part is a cheap habit.
Keep the easy work nasal when you can. Zone 2 pace in the cold is where the nose has the best chance of doing its job.
On the coldest days, cover mouth and nose loosely with a scarf or neck tube. It follows the same idea as an HME. I did not find a trial testing scarves, so treat it as reasonable, not proven.
Shift the hardest intervals to milder hours or indoors when it is far below freezing. Carlsen suggests that endurance competitions should not be held below minus 15 °C, which tells you how seriously clinicians take the cold.
If you cough, wheeze or feel tight in the chest during or after cold-weather sessions, get it checked. According to Ora and colleagues, resting lung function is often normal in athletes, so diagnosis needs an exercise or indirect provocation test.
Short answers
Is it bad to breathe cold air while running?
For many healthy people, cold-weather sessions are tolerated well. In the 2022 treadmill study at about minus 15 °C, none of the 23 healthy adults reached the clinical threshold for bronchoconstriction, although lung function dipped slightly. Recurring symptoms are a reason to see a doctor.
Should I breathe through my nose or mouth in the cold?
Nose where the effort allows, mouth when it does not. The skill is choosing the switch on purpose.
Cold air asks more of your airways, and the studies suggest that warming the air you inhale reduces that load. Your lungs do not need heroics at minus 10 degrees, they need a patient start.
This article is for general information and does not replace medical advice. If you have persistent cough, wheeze or breathlessness, please have it checked by a doctor.
Sources
- Carlsen KH (2012). Sports in extreme conditions: the impact of exercise in cold temperatures on asthma and bronchial hyperresponsiveness in athletes. British Journal of Sports Medicine 46:796-799. Link
- Nisar M, Spence DP, West D, Haycock J, Jones Y, Walshaw MJ, Earis JE, Calverley PM, Pearson MG (1992). A mask to modify inspired air temperature and humidity and its effect on exercise induced asthma. Thorax 47(6). Link
- Jackson AR, Hull JH, Hopker JG, Fletcher H, Gowers W, Birring SS, Dickinson JW (2020). The impact of a heat and moisture exchange mask on respiratory symptoms and airway response to exercise in asthma. ERJ Open Research. PubMed
- Stenfors N, Persson H, Tutt A, Tufvesson E, Andersson EP, Ainegren M, Hanstock HG (2022). A breathing mask attenuates acute airway responses to exercise in sub-zero environment in healthy subjects. European Journal of Applied Physiology. DOI
- Ora J, De Marco P, Gabriele M, Cazzola M, Rogliani P (2024). Exercise-induced asthma: managing respiratory issues in athletes. Journal of Functional Morphology and Kinesiology 9(1):15. DOI