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Reference topic 10: The Breath You Forgot How to Take

Nose breathing vs mouth breathing: what the evidence says

ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.49 sources6 graded recommendationsTopic hub: MovementTopic hub: Stress and the mind

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Luciano Bernardi's team in Pavia and Florence was studying how reading and mental arithmetic, done silently or aloud, stir the heart's rhythms. As a less arousing comparison, they used the rosary, and the comparison surprised them. Each cycle of the Ave Maria, recited in Latin, unrehearsed, pause included, took very nearly 10 seconds.1

A cycle is normally spoken on one slow breath: six breaths a minute. Left alone, the team's 23 healthy volunteers took about 14 breaths a minute. The prayer and a yoga mantra both slowed them to close to six. At that pace, heart rate, blood pressure and even blood flow in the brain rose and fell together, in waves timed to the breath. Baroreflex sensitivity, a measure of how briskly the heart answers each change in blood pressure, was about a fifth higher during the prayer than during free talking.1

Mismatch card

The system

Breathing: the nose as the default airway, and the breath as a lever on heart rhythm.

What it expects

An open nose at rest and in sleep, with the mouth joining in for hard effort.

What it gets

Noses often blocked by allergy, which pushes breathing to the mouth, and breathing hacks that outpace their trials.

What happens in the gap

When the mouth takes over in sleep, the throat collapses more easily: snoring, apneas and oxygen dips.

The handrail

Nasal breathing and treating a blocked nose (●●○); slow, exhale-weighted breathing (●●○)

Strength of evidence

●●○ Experiments show that blocked noses disrupt sleep and trials show modest benefits of slow breathing, but long-term hard outcomes are untested.

What this topic covers

  • ·The Default Airway
  • ·The Sinus Factory
  • ·Ten Men With Blocked Noses
  • ·Six Breaths a Minute
  • ·The Nijmegen Experiment

The practical version is in the book: Chapter 13, Stress and the Mind.

The handrail

Each recommendation carries the strength of the evidence behind it. How the grades work.

  1. Let your nose do the default work

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    Breathe through it at rest, walking and asleep. Mouth breathing in hard exercise is normal, and nose-only breathing lowers peak output.947 If your nose is usually blocked, have the cause treated.21

  2. Slow, exhale-weighted breathing

    ProbableEvidence grade: Probable. Good observational evidence with a plausible mechanism, or small or few trials.

    About five or six breaths a minute (say, four seconds in and six out) for 5-10 minutes, on most days; the blood-pressure trials ran for at least four weeks. Heart-rate variability rises during practice (●●●); stress and blood-pressure benefits are modest.283241 An app, a count or a rhythmic prayer can keep time.1

  3. Cyclic sighing for a quick reset

    EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.

    Inhale slowly through the nose, top up with a second short inhale, then exhale slowly and fully through the mouth, for up to five minutes.23

  4. Snoring with daytime sleepiness or witnessed pauses

    EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.

    Get a sleep assessment before trying mouth tape. Never tape a blocked nose, and skip tape when you feel sick: sleep specialists worry about vomiting and inhaling it.4319 Under medical supervision, tape has helped some mouth-breathers stick with their CPAP (continuous positive airway pressure) machines for sleep apnea (●●○).48

  5. Hyperventilation and breath-holds: only sitting or lying on dry land

    EmergingEvidence grade: Emerging. Early, small, animal-only, or actively contested.

    Never practice them in or near water, in the bath or while driving. Skip them if you are pregnant or have heart disease or a seizure disorder, and stop if you feel dizzy: low carbon dioxide narrows the brain's blood vessels.392349

  6. Keep your treatment

    Breathing practice complements care for asthma, high blood pressure, anxiety and depression; it never replaces it.33

The skeptic's corner

The case against this topic, from the research itself.

Nasal breathing's reputation outruns its data in places. The oxygen gain from sinus nitric oxide rests on a handful of people. In a small randomized trial in heart-surgery patients, nasal breathing lowered resistance in the lungs' blood vessels but left arterial oxygen unchanged.40 No one measured how Paleolithic (Old Stone Age) people breathed, so the popular claim that modern people breathe faster or shallower than their ancestors is a guess.

Breathwork helps, a little. A meta-analysis of randomized trials found small-to-moderate reductions in stress, anxiety and depressive symptoms. Most of the trials were at moderate risk of bias, and the authors warned against "a miscalibration between hype and evidence."41 The cyclic-sighing trial was not registered in advance, drew mostly on one psychology class, and used videos recorded by its senior author, Andrew Huberman. It found no change in heart-rate variability.23 In one review, device-guided breathing for blood pressure lost its effect once the trials sponsored by or involving the manufacturer were set aside.42

A recent review of mouth taping, a social-media fad, found 10 studies, only two positive, and warned of "a potentially serious risk of harm for individuals indiscriminately practicing this trend" (Topic 38).43 Nearly every randomized trial of the Wim Hof method, Nijmegen's included, carries a high risk of bias, mostly because participants cannot be blinded to what they are doing.44 In one trial, 15 days of daily practice changed no cardiovascular or psychological measure.45 In another, among midlife women with high stress and depressive symptoms, the method matched but did not beat slow breathing. Both groups improved, and all six dropouts came from the Wim Hof group.46 Large trials, registered in advance and tracking blood pressure, heart disease or depression for a year or more, would show what slow breathing is worth.

Terms this topic defines

Related topics

Sources cited above

  1. 1.Bernardi, L., Sleight, P., Bandinelli, G., Cencetti, S., et al. (2001). "Effect of rosary prayer and yoga mantras on autonomic cardiovascular rhythms: comparative study." BMJ, 323(7327), 1446-1449. https://doi.org/10.1136/bmj.323.7327.1446 (baroreflex sensitivity 9.5 ms/mmHg during free talking, 11.5 during the Ave Maria; breathing 5.6 per minute during the Ave Maria). (23 volunteers: 16 men and seven women; conditions included free breathing, breathing to a metronome, free talking, the Ave Maria and a yoga mantra)
  2. 40.Settergren, G., Angdin, M., Astudillo, R., Gelinder, S., et al. (1998). "Decreased pulmonary vascular resistance during nasal breathing: modulation by endogenous nitric oxide from the paranasal sinuses." Acta Physiologica Scandinavica, 163(3), 235-239. https://doi.org/10.1046/j.1365-201x.1998.00352.x (randomized crossover, n=10)
  3. 41.Fincham, G.W., Strauss, C., Montero-Marin, J., and Cavanagh, K. (2023). "Effect of breathwork on stress and mental health: a meta-analysis of randomised-controlled trials." Scientific Reports, 13(1), 432. https://doi.org/10.1038/s41598-022-27247-y
  4. 23.Balban, M.Y., Neri, E., Kogon, M.M., Weed, L., et al. (2023). "Brief structured respiration practices enhance mood and reduce physiological arousal." Cell Reports Medicine, 4(1), 100895. https://doi.org/10.1016/j.xcrm.2022.100895 (registered retrospectively, NCT05304000).
  5. 42.Mahtani, K.R., Nunan, D., and Heneghan, C.J. (2012). "Device-guided breathing exercises in the control of human blood pressure: systematic review and meta-analysis." Journal of Hypertension, 30(5), 852-860. https://doi.org/10.1097/HJH.0b013e3283520077 (eight trials, five of them sponsored by or involving the manufacturer)
  6. 43.Rhee, J., Iansavitchene, A., Mannala, S., Graham, M.E., et al. (2025). "Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: a systematic review." PLOS ONE, 20(5), e0323643. https://doi.org/10.1371/journal.pone.0323643
  7. 44.Almahayni, O., and Hammond, L. (2024). "Does the Wim Hof Method have a beneficial impact on physiological and psychological outcomes in healthy and non-healthy participants? A systematic review." PLOS ONE, 19(3), e0286933. https://doi.org/10.1371/journal.pone.0286933 (every randomized trial rated "high concerns" for bias except one, a sprint-performance pilot rated "some concerns").
  8. 45.Ketelhut, S., Querciagrossa, D., Bisang, X., Metry, X., et al. (2023). "The effectiveness of the Wim Hof method on cardiac autonomic function, blood pressure, arterial compliance, and different psychological parameters." Scientific Reports, 13(1), 17517. https://doi.org/10.1038/s41598-023-44902-0 (n=42)
  9. 46.Blades, R., Mendes, W.B., Don, B.P., Mayer, S.E., et al. (2024). "A randomized controlled clinical trial of a Wim Hof Method intervention in women with high depressive symptoms." Comprehensive Psychoneuroendocrinology, 20, 100272. https://doi.org/10.1016/j.cpnec.2024.100272 (n=84; outcomes were depression, anxiety and stress)
  10. 9.Niinimaa, V., Cole, P., Mintz, S., and Shephard, R.J. (1980). "The switching point from nasal to oronasal breathing." Respiration Physiology, 42(1), 61-71. https://doi.org/10.1016/0034-5687(80)90104-8 (20 of 30 switched to nose-plus-mouth breathing at a moderate effort; five stayed nose-only throughout; four used both routes from the start)
  11. 47.Mapelli, M., Salvioni, E., Mattavelli, I., Grilli, G., et al. (2025). "Nasal vs. oral BREATHing WIn Strategies in healthy individuals during cardiorespiratory Exercise testing (BreathWISE)." PLOS ONE, 20(7), e0326661. https://doi.org/10.1371/journal.pone.0326661
  12. 21.Bousquet, J., Anto, J.M., Bachert, C., Baiardini, I., et al. (2020). "Allergic rhinitis." Nature Reviews Disease Primers, 6(1), 95. https://doi.org/10.1038/s41572-020-00227-0
  13. 28.Laborde, S., Allen, M.S., Borges, U., Dosseville, F., et al. (2022). "Effects of voluntary slow breathing on heart rate and heart rate variability: a systematic review and a meta-analysis." Neuroscience and Biobehavioral Reviews, 138, 104711. https://doi.org/10.1016/j.neubiorev.2022.104711
  14. 32.Chaddha, A., Modaff, D., Hooper-Lane, C., and Feldstein, D.A. (2019). "Device and non-device-guided slow breathing to reduce blood pressure: a systematic review and meta-analysis." Complementary Therapies in Medicine, 45, 179-184. https://doi.org/10.1016/j.ctim.2019.03.005 (17 randomized trials; systolic pressure about 5.6 mmHg and diastolic about 3 mmHg lower)
  15. 19.Roy, S. (2020). "A Popular New Book Elicits Gasps of Delight & Concern from Sleep Specialists." Sleep Review, 4 December 2020. https://sleepreviewmag.com/sleep-health/sleep-whole-body/lungs/breath-james-nestor-sleep-medicine/ (the post-experiment figures are the article's summary of Nestor's account).
  16. 48.Meksukree, A., Pitipanyakul, S., Laohavinij, W., Chaitusaney, B., et al. (2025). "The role of mouth tape for CPAP use in patients with mouth breathing and OSA." Journal of Clinical Sleep Medicine, 21(12), 2063-2071. https://doi.org/10.5664/jcsm.11870
  17. 39.Wim Hof Method (2026). What Is Shallow Water Blackout? https://www.wimhofmethod.com/what-is-shallow-water-blackout (accessed 19 September 2026). (the guidance reads: "Never practice the Wim Hof Method (or any other forms of deep) breathing ahead of or during immersion in or over water, when piloting a vehicle, or in any other situation where loss of consciousness could cause harm to yourself or others.")
  18. 49.Ainslie, P.N., and Duffin, J. (2009). "Integration of cerebrovascular CO2 reactivity and chemoreflex control of breathing: mechanisms of regulation, measurement, and interpretation." American Journal of Physiology: Regulatory, Integrative and Comparative Physiology, 296(5), R1473-R1495. https://doi.org/10.1152/ajpregu.91008.2008
  19. 33.Bruton, A., Lee, A., Yardley, L., Raftery, J., et al. (2018). "Physiotherapy breathing retraining for asthma: a randomised controlled trial." The Lancet Respiratory Medicine, 6(1), 19-28. https://doi.org/10.1016/S2213-2600(17)30474-5 (n=655 adults with incompletely controlled asthma; outcomes at 12 months)

This topic carries 49 notes in the research manuscript; the 19 above are those behind the material on this page. Full source register.