7 min read 

At a Glance

Summer heat triggers an involuntary increase in breathing rate called thermal hyperpnea: your body's attempt to cool itself using your respiratory system. Hot, humid air also makes heat harder to shed and delivers a slightly lower partial pressure of oxygen per breath. The result is faster, shallower, chest-driven breathing that suppresses the parasympathetic nervous system. Three breathwork practices: Sitali, the 5-5 reset, and the belly-breath check — can interrupt this stress cycle and restore calmer breathing.

In this article, you'll discover:

• The physiology behind why heat makes breathing feel harder, and why it drains you 
• What thermal hyperpnea is, and why your body triggers it automatically 
• Why hot, humid air compounds the problem beyond just temperature 
• Three practical breathwork tools calibrated for heat: Sitali, the 5-5 reset, and the belly-breath check 
• A simple awareness practice to build a better relationship with your breath in hot conditions 

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Table of Contents

What Heat Actually Does to Your Breath 

• The thermoregulation demand 
• Why humid air compounds the problem 

Thermal Hyperpnea: The Breathing Response You Did Not Ask For 

• What the research shows 
• What hyperpnea does downstream 

Three Breathwork Practices for Hot Days 

• Sitali: the cooling breath 
• The 5-5 reset 
• The belly-breath check 

Your Heat-Breath Awareness Practice 

Key Takeaways 

Frequently Asked Questions 

Conclusion 

Related Articles 

References 

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 Last week, my mother-in-law was lying down in the afternoon, too exhausted to move. 

“The heat is unbearable,” she said. “I just feel so restless.” 

Just that uneasy, can-not-settle feeling when your body is overwhelmed and does not know where to put itself. If you have felt that this summer, whether you are in Chennai or California, Singapore or Spain, here is what nobody tells you: 

That stuck, heavy feeling has a name. And once you understand what is causing it, you can actually do something about it. 

What Heat Actually Does to Your Breath

The thermoregulation demand

When temperatures climb, your body has one urgent job: cool itself down. To do that, it borrows energy, and borrowed energy demands more oxygen. 

So your breathing speeds up. Shallower. Faster. Chest-driven. 

At the same time, your body reroutes blood toward the skin to release heat through radiation and sweating. Research tracking participants at rest in 40°C conditions found that minute ventilation (the total volume of air breathed per minute) increased by up to 78% compared to baseline, and this happened without any physical exertion at all.¹

Even simple tasks can feel surprisingly exhausting on hot days. That is not weakness. It is your body allocating resources to an emergency it did not ask for. 

Why humid air compounds the problem

Hot, humid air adds another layer. Water vapor in air displaces dry air, which means each breath delivers a slightly lower partial pressure of oxygen. The effect is modest but real and in high humidity, your body’s primary heat-dissipation mechanism (sweating) becomes far less efficient because sweat can no longer evaporate readily.² 

Research confirms that as relative humidity rises, evaporative heat loss drops substantially. One study found that sweating efficiency fell from 0.50 in low-humidity conditions to 0.16 in very high humidity, meaning the body retains significantly more heat.² You are working harder to breathe, losing less heat per breath, and feeling the result as a thick, oppressive heaviness that no fan seems to fix. 

Add in stagnant air, which traps ground-level ozone and particulates at higher concentrations in summer heat’s atmospheric inversions, and each breath carries additional airway irritants alongside the temperature stress. 

Thermal Hyperpnea: The Breathing Response You Did Not Ask For

What the research shows

Scientists call the heat-triggered increase in breathing rate thermal hyperpnea. It is not hypothetical; it is a well-characterized physiological response in which both the rate and depth of breathing increase as core temperature rises.³ 

A key study published in Physiological Reports demonstrated that in passively heated humans, minute ventilation increased linearly as core (esophageal) temperature rose above approximately 38°C. Crucially, the researchers also showed that this spontaneous hyperventilation can be substantially reduced through voluntary breath control, and doing so attenuated the downstream reduction in CO2 and cerebral blood flow that normally follows.⁴  

That last point matters for everyone, not just researchers: the breathing response heat triggers is involuntary, but it is not unstoppable. Conscious breath practice can intervene. 

What hyperpnea does downstream

Thermal hyperpnea does two things that explain the broader misery of hot days: 

1. It suppresses parasympathetic activity. Your autonomic nervous system has two modes: the sympathetic (fight-or-flight, alert, mobilized) and the parasympathetic (rest-and-digest, calm, restorative). Faster, shallower chest breathing is associated with sympathetic dominance. Once hyperpnea takes over, the calmer side starts losing ground. That is why heat does not just make you physically uncomfortable, it makes you more irritable, more fatigued, more cognitively foggy. 

2. It lowers CO2 and reduces cerebral blood flow. Hyperpnea blows off more CO2 than your body needs to release, which narrows blood vessels slightly and reduces blood flow to the brain.⁴ The result is not just tired legs, it is a foggy, unsettled quality of thinking that compounds the physical discomfort. 

Your body started all of this. Breath practice is how you talk back. 

Three Breathwork Practices for Hot Days

Conscious breathwork is, at its core, a way of taking back voluntary control from a stress response your environment is triggering. 

Here are three practices worth reaching for when the heat climbs. 

1. Sitali — the cooling breath

Sitali (also spelled Sheetali) is a classical pranayama technique specifically designated in traditional yogic texts for heat and pitta imbalance. Swami Satyananda Saraswati’s Asana Pranayama Mudra Bandha describes it as inducing muscular relaxation, reducing emotional excitation, and activating brain centers associated with temperature regulation. 

How to practise: Roll your tongue into a tube shape (if your tongue does not curl, purse your lips slightly as if sipping through a straw, this is the Sitkari variation). Inhale slowly and deeply through that opening. Close the mouth and exhale through the nose. Six to eight rounds, ideally indoors in the coolest part of your day. 

The mechanism: you are pulling air over a moist mucosal surface before it reaches your lungs, creating mild evaporative cooling at the mouth. More importantly, the slow, controlled inhalation slows your overall breathing rate and shifts the nervous system toward parasympathetic activation.⁵ 

A 2014 EEG study of Sheetali and Sitkari pranayama found notable decreases in beta-wave power (associated with anxiety and agitation) and increases in alpha, delta, and theta wave activity (associated with calm, relaxed states).⁶ Emerging research is beginning to characterize the autonomic mechanisms involved, though the evidence base for specific physiological cooling effects in healthy adults remains an active area of investigation. The calming effect, however, is consistent across available studies. 

Note: Sitali is traditionally practised in clean air. On high-pollution days, breathing outdoors through an open mouth may introduce more irritants than the practice offsets. Keep this practice indoors on bad air quality days. 

2. The 5-5 reset

Inhale through your nose for five counts. Exhale for five counts. That is all. 

Slow, rhythmic breathing at approximately five to six breaths per minute is one of the most consistently studied mechanisms for activating the parasympathetic nervous system. Research shows this pacing increases heart rate variability, reduces cortisol, and supports parasympathetic dominance.⁷ 

Heat has already pushed your system toward sympathetic overdrive. Five minutes of the 5-5 pattern in the coolest part of your day — early morning, an air-conditioned room, a shaded space — works as a deliberate counterweight. Your nervous system does not spontaneously find calm in heat. You have to offer it the conditions. 

You can also link this to the stair-climbing principle covered in this article on exercise and breath capacity: rhythm connects breath to movement and teaches your nervous system to work more efficiently. 

3. The belly-breath check

Place one hand on your belly. Inhale so the hand rises, not your chest. 

Heat automatically triggers chest-driven breathing. Chest breathing is your body’s emergency mode: it prioritizes rapid oxygen intake over efficiency or calm. Diaphragmatic breathing is the off switch. 

Slow diaphragmatic breathing has been shown in multiple RCTs to reduce cortisol, increase parasympathetic activation (measured via HRV), and lower inflammatory markers.⁸ Mechanically, belly breathing allows the diaphragm, your primary breathing muscle, to fully descend, creating space for maximal lung expansion rather than the shallow thoracic breathing that heat triggers. 

You do not need a timer or a practice session. Just notice when your breath has moved to your chest, and consciously move it back down. Three belly breaths takes twenty seconds. The nervous system effect may start immediately. 

Your Heat-Breath Awareness Practice

Before you reach for any specific technique, try noticing first: 

• When does your breathing feel heavier: outdoors vs. indoors? 
• Are you taking shorter, faster inhales without realising it? 
• What time of day does your breath feel most effortless? 

Heat does not make you breathe wrong. It reveals patterns already there, just louder. Chest-breathing, mouth-breathing, breath-holding under physical effort: these tendencies exist year-round. Summer amplifies them long enough for you to see them. 

That visibility is an opening. As explored in the overview of breathing habits and conscious awareness, awareness of a pattern is the first step to changing it. Heat is just a particularly honest teacher. 

Key Takeaways

• Heat triggers thermal hyperpnea: an involuntary increase in breathing rate and depth as your body attempts to cool itself. Research shows minute ventilation can rise by up to 78% at rest in hot conditions, with no physical exertion required. 
• Hot, humid air reduces both oxygen partial pressure per breath and your body’s ability to shed heat through sweating, compounding the respiratory burden. 
• Thermal hyperpnea suppresses parasympathetic activity and lowers cerebral blood flow, which explains the fatigue, irritability, and mental fog that accompany hot days, beyond just the temperature. 
• Voluntary breath control can significantly reduce heat-induced hyperventilation. Three practices are particularly well-suited to hot conditions: Sitali (cooling breath), the 5-5 reset, and the belly-breath check. 
• Summer breathing patterns reveal habitual tendencies already present year-round. Heat is a useful diagnostic: what you notice, you can change. 

Frequently Asked Questions

What is thermal hyperpnea?

Thermal hyperpnea is the involuntary increase in both breathing rate and tidal volume (depth) that occurs as core body temperature rises. It appears to serve a heat-loss function, helping the body expel heat through the respiratory system. It is documented in humans and is distinct from simple panting (tachypnea), which is more common in other mammals. The cause remains an active area of research, with carotid chemoreceptors and central thermoregulation pathways both appearing to play a role. 

Does humidity actually reduce the oxygen in the air?

In practical terms, yes, slightly. Water vapor molecules displace dry air molecules, meaning the partial pressure of oxygen per unit of air is marginally lower in humid conditions than in dry air at the same temperature. The more significant mechanism, however, is that high humidity prevents sweat from evaporating, which traps heat in the body and forces the cardiovascular and respiratory systems to work harder to compensate. The felt difficulty of breathing in humid heat is real and physiologically grounded. 

Why does heat make me irritable and foggy, not just physically uncomfortable?

Heat-induced hyperpnea pushes the autonomic nervous system toward sympathetic dominance (fight-or-flight mode). This suppresses the parasympathetic functions associated with calm, clear thinking, and emotional regulation. Simultaneously, hyperpnea blows off more CO2 than the body needs to lose, which narrows blood vessels slightly and reduces cerebral blood flow. Both mechanisms contribute to the cognitive and emotional effects of extreme heat. 

Can Sitali actually cool the body down?

Traditional yogic texts attribute a literal cooling effect to Sitali. The evidence from modern research is more nuanced: the mild evaporative cooling at the mouth is real but modest; the dominant mechanism is likely the parasympathetic shift produced by slow, controlled breathing. Whether Sitali cools the body in a measurable core-temperature sense or primarily soothes the nervous system’s heat-stress response is still an open question in the research. What is consistent across studies is the calming, anxiety-reducing effect. That alone is worth six to eight rounds on a hot day. 

I feel fine in heat. Do I still need to practice breath awareness?

Feeling fine does not mean your breathing is unaffected, it means your body is compensating effectively, for now. Heat-related physiological changes (faster breathing, sympathetic bias, blood redistribution) happen automatically regardless of whether you consciously notice discomfort. Breath awareness in heat is less about correcting a problem and more about building the capacity to notice and influence these automatic responses before they accumulate into fatigue or overstress. It is preventive maintenance, not crisis intervention. 

When is the best time to practise breathwork in summer?

Early morning, before peak heat, is the optimal window: air quality is typically better, temperatures are lower, and your body has had the night to recover its thermoregulatory baseline. Avoid peak heat hours (typically 11am to 4pm) for any extended breath practice that involves outdoor air or exertion. Sitali and the 5-5 reset can be practised indoors any time of day. The belly-breath check can be done silently, anywhere, at any moment of the day. 

Is breathwork safe during a heat wave?

The three practices described here, Sitali, the 5-5 reset, and the belly-breath check, are gentle, low-intensity techniques appropriate for healthy adults in hot conditions. They do not involve breath-holding or hyperventilation. As with any activity in extreme heat, stay indoors in a cool environment where possible, stay hydrated, and do not continue any practice that produces dizziness, chest tightness, or unusual discomfort. If you have asthma, COPD, or other respiratory conditions, extreme heat days warrant extra caution and consultation with your healthcare provider. 

Conclusion

Every labored breath in summer heat is your body saying: slow down, I am doing more than you know. 

That restless, can-not-settle exhaustion my mother-in-law described is not weakness, and it is not just the temperature number on a thermometer. It is the downstream effect of a nervous system pushed into overdrive by a cooling demand it cannot quite meet, expressed through the mechanism it uses constantly without your permission: your breath. 

The research is clear that heat-induced hyperventilation, while involuntary, can be substantially reduced by conscious breath control. Three simple practices, the cooling architecture of Sitali, the pacing intervention of the 5-5 reset, and the simple redirect of the belly-breath check, are available to anyone, anytime, without equipment. 

Summer is not just meteorology. It is your body asking for a little more attention this season. 

Start with one practice. Notice what shifts. The breath that feels heavy in heat is still, fundamentally, yours to work with. 

Related Articles

• Why Winter Air Makes Breathing Harder (And How to Breathe Easier) 
• Why Breathing Less Can Calm You More: The Science of CO₂-Optimized Breathing 
• Nose Breathing vs Mouth Breathing: Why Your Breathing Technique Matters 
• What Does Shortness of Breath on Stairs Mean? 
• Spotting Your Breathing Habits: A Complete Guide to Conscious Breath Awareness 

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References

1. Henderson MET, Brayson D, Halsey LG. The cardio-respiratory effects of passive heating and the human thermoneutral zone. Physiol Rep. 2021 Aug;9(16):e14973. doi: 10.14814/phy2.14973. PMID: 34409765; PMCID: PMC8374383. https://pmc.ncbi.nlm.nih.gov/articles/PMC8374383/
2.  Bright FM, Clark B, Jay O, Périard JD. Elevated Humidity Impairs Evaporative Heat Loss and Self-Paced Exercise Performance in the Heat. Scand J Med Sci Sports. 2025 Mar;35(3):e70041. doi: 10.1111/sms.70041. PMID: 40107869; PMCID: PMC11922688. https://doi.org/10.1016/j.jtherbio.2024.103990 
3. White, M. D. (2006). Components and mechanisms of thermal hyperpnea. Journal of Applied Physiology, 101(2), 655–663. https://doi.org/10.1152/japplphysiol.00210.2006 
4. Tsuji, B., Hoshi, Y., Honda, Y., Fujii, N., Sasaki, Y., Cheung, S. S., Kondo, N., & Nishiyasu, T. (2019). Respiratory mechanics and cerebral blood flow during heat-induced hyperventilation and its voluntary suppression in passively heated humans. Physiological Reports, 7(1), e13967. https://doi.org/10.14814/phy2.13967 
5. Saraswati, S. S. (1996). Asana pranayama mudra bandha (3rd ed.). Bihar School of Yoga. 
6. Bhavanani, A. B., Sanjay, Z., & Madanmohan. (2014). Effect of sheetali and sheetkari pranayama on electroencephalographic (EEG) activity. IOSR Journal of Pharmacy, 4(1), 10–16. 
7. Little, S., Bleakley, C., & O’Neill, S. (2025). The A52 breath method: A narrative review of breathwork for mental health and stress resilience. Stress and Health. https://doi.org/10.1002/smi.70098 
8. Maniaci, A., Iannella, G., Vicini, C., Pavone, C., Nacci, A., Romeo, S., & Lentini, M. (2024). Neurobiological and anti-inflammatory effects of a deep diaphragmatic breathing technique based on neofunctional psychotherapy: A pilot RCT. Stress and Health, 40(6), e3503. https://doi.org/10.1002/smi.3503 

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About the Author

Written by Sowmiya Sree | Breath Researcher & Author 

This article is thoroughly researched and fact-checked using peer-reviewed studies and trusted medical resources. 

Last updated: June 2026 

Medical Disclaimer

This article is for informational purposes only and does not constitute medical advice. The breathwork techniques described are gentle practices suitable for healthy adults; they are not a treatment for heat-related illness, respiratory conditions, or any medical diagnosis. If you experience chest pain, difficulty breathing, dizziness, or symptoms of heat exhaustion or heat stroke, seek medical attention immediately. Always consult a qualified healthcare professional before beginning new breathing practices if you have asthma, COPD, cardiovascular disease, low blood pressure, or any other relevant health condition. 

Photo by  PraewBlackWhile @ Canva