Maybe—but not the way you might expect!
By Bernie Clark
July 16, 2023
Can yoga help to cool us down when the temperature goes up? Killer heat domes are becoming more common, hotter and last longer as the planet continues to warm. In yoga lore it is believed that some forms of yoga pranayama practices, such as sheetali and sheetkari can cool the body. According to studies done in recent years at the Patanjali Research Foundation in Haridwar, India, “The results do not support the description of these yoga breathing practices as cooling.”1 The findings showed that these pranayama practices actually warm us up. What does work to cool the body? Quietly lying down on the back with eyes closed, breathing through the nose without any directed awareness!
Thermoregulation
When the temperature hits 100F or 37.8C, it is hot! Whether this is in a heated yoga room or the ambient temperature outside, the body needs to be cooled down. Our inner temperature is managed within a very small window: generally, between 97-99F or 36.1-37.2C. This level of inner heat is created through the daily activities of our cells. Our muscles, for example, burn fuel and oxygen to produce the energy needed to move the body, and a by-product of this cellular activity is heat. Our cells are so proficient at producing heat that we have more heat than we need, so a way must be found to shed this excess internal heat. This is the reason we prefer to be in a room averaging around 74F (24C).2 We naturally cool off when we are in a room at this temperature, but it is not so low that we have to turn up our inner furnace to stay at this happy medium.
Why does the body need to be so warm? It takes a lot of energy to keep us at this temperature, but evolution has shown that if we are much cooler, fungus grows too easily. At 98F or 37C, most fungi die. If we could get hotter, we would kill all fungus, but there is a law of diminishing returns: it is energetically expensive to heat the body and our current levels seem to be an ideal trade-off between killing pathogens and saving energy.3
The hypothalamus, a small structure in the brain which regulates temperature, hunger, mood and other states of the body, integrates input from sensors reporting on our internal temperature. If we are not dissipating the excess heat that our cells are producing quickly enough, the hypothalamus senses an increase in core temperature and triggers four different cooling mechanisms: convection, radiation, conduction and evaporation which we fondly call “sweating”.
The four mechanisms for cooling down
Convection is the transfer of heat through the movement of air or water. For us, this primarily refers to the transfer of heat from the body’s surface to the surrounding air. When the body temperature rises, blood vessels near the skin’s surface dilate, allowing more blood to flow through them. As this warm blood reaches the skin, it transfers heat to the surrounding air through convection. A slight breeze or wind enhances this cooling effect by increasing the air movement and facilitating the transfer of heat away from the body.
Radiation is the transfer of heat through electromagnetic waves. Radiation is responsible for the majority of our heat loss because we naturally emit infrared radiation. When the body’s temperature is higher than its surroundings, we radiate heat away to cooler objects or the surrounding environment. When you stand near a cooler object, such as a cold wall or in front of a fan, you can feel a cooling sensation as the body’s heat is transferred to those objects via radiation.
Conduction refers to the transfer of heat between two objects that are in direct contact with each other. This is a minor role in comparison to convection and radiation. However, if the body comes into contact with a colder surface, such as holding a cold beer, heat can be conducted away from the body, aiding in cooling.
Evaporation is a process by which liquid changes into a gas. When the body gets too hot, sweat glands produce sweat, which consists mainly of water and small amounts of dissolved salts and other substances. As the sweat evaporates from the skin’s surface, it absorbs heat from the body, resulting in cooling. This process is highly effective in hot and dry conditions but can be less efficient in humid environments where the air is already saturated with moisture. Of course, if you sweat for too long or too much, you will start to become dehydrated and will also lose the essential electrolytes that are secreted in the sweat. When you are hot, you need to keep consuming water and electrolytes.
Sheetal in Sanskrit means “cool”
The power of evaporation to remove heat from the body is the explanation for sheetali’s purported prowess to cool the body. The practice is done by sticking out your tongue, curling the sides of the tongue into a tube and breathing in through that tube. If you try it right now, you will probably notice a distinct cooling effect. Moisture on your tongue is evaporating which takes away heat. It feels cool. There are also some other benefits suggested from this practice, such as reducing blood pressure, heart rate and breathing rate.4 For those incapable of curling the tongue into a tube, Sheetkari is similar. Instead of sticking out your tongue, you close your teeth together, pull back your lips as wide as possible and breathe in through your closed dentures. This will make a hissing sound and should still feel cooling. (In both practices, breathe out through the nose.)
Psychologically, you may interpret the cooling sensations in your mouth as a sign that your whole body is cooling down, but unfortunately, breathing in this manner actually uses more energy than you lose. Mouth breathing and the muscular effort involved in these pranayamas causes the body to heat up more than if you didn’t breathe like this.
What does work? Lying on your back in shavasana and allowing your breath to come and go without effort and without monitoring. The studies done at the Patanjali Research Foundation has found that quiet breathing while lying down cools the body, reduces oxygen consumption and decreases carbon dioxide production, all signs that the body is working less and generating less heat. Even compared to mindfully breathing, unmonitored breathing is cooler. Plus, lying down on the floor is where the coolest air is. Stay low, stay cool, and drink.
Since sweating is such a powerful tool for cooling the body, drinking warm liquids seems to be better than cold drinks. While cold drinks feel good going down, and they do temporarily cool the core of the body, when the core feels cooler, the hypothalamus (remember it?) starts to slow down the rate of sweating. Sweating cools us better than cold drinks. At least that was the findings of a 2012 study when sweating was the primary tool for cooling down.5 That means in hot and arid environments, where sweating works really well, hot drinks will cool you more than cold drinks. In very humid environments, where sweating does not work as well, colder drinks may work better, but try the shavasana approach as well.
Stay cool everyone!
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[1] Telles S, Gandharva K, Sharma SK, Gupta RK, Balkrishna A. Body Temperature and Energy Expenditure During and After Yoga Breathing Practices Traditionally Described as Cooling. Med Sci Monit Basic Res. 2020 Jan 7;26:e920107. doi: 10.12659/MSMBR.920107. PMID: 31907342; PMCID: PMC6977599.
[2] Beware of averages! Most women would prefer a room temperature of 77F while men like it better at 71F. The more dense the body, the greater the amount of heat retained and thus the lower the ambient temperature needed to balance the energy within and without. Men, on average are denser than women and thus prefer a cooler ambient temperature. See https://www.discovermagazine.com/mind/room-temperatures-set-for-mens-comfort-may-disadvantage-women-study-finds.
[3] Bergman A, Casadevall A. Mammalian endothermy optimally restricts fungi and metabolic costs. mBio. 2010 Nov 9;1(5):e00212-10. doi: 10.1128/mBio.00212-10. PMID: 21060737; PMCID: PMC2975364.
[4] Shetty P, Reddy B KK, Lakshmeesha DR, Shetty SP, Kumar G S, Bradley R. Effects of Sheetali and Sheetkari Pranayamas on Blood Pressure and Autonomic Function in Hypertensive Patients. Integr Med (Encinitas). 2017 Oct;16(5):32-37. PMID: 30936803; PMCID: PMC6438091.
[5] Bain AR, Lesperance NC, Jay O. Body heat storage during physical activity is lower with hot fluid ingestion under conditions that permit full evaporation. Acta Physiol (Oxf). 2012 Oct;206(2):98-108. doi: 10.1111/j.1748-1716.2012.02452.x. Epub 2012 Jun 9. PMID: 22574769.