heat

When to Use Ice, When to Use Heat

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(xmee/iStock)

Applying ice or heat can provide relief from injuries, aches, and pains, but they shouldn’t be used interchangeably. Generally speaking, ice works well after a sudden injury while heat helps to soothe ongoing muscle aches and pains.

Ice works for injuries because it narrows your blood vessels, which helps prevent blood from accumulating at the site of injury, which will add to inflammation and swelling while delaying healing. This is also why elevation is helpful, since it  limits blood flow to the area to minimize swelling.

A good rule of thumb to remember following an injury is RICE: rest, ice, compression, and elevation. You should generally ice the area for 48 to 72 hours to reduce secondary tissue damage and ease pain.

Ice should be applied for about 20 minutes once an hour. You don’t want to use ice longer than this as it could damage your skin or even lead to frostbite. Be sure the ice or gel pack you use can be wrapped around the injured area and even compressed to minimize swelling. You’ll want to protect your skin from direct exposure  by applying a cloth or towel between your skin and the ice.

When to Use Heat…

For muscle aches and pains, applying a heat pack will help bring blood flow to the area, which promotes healing and soothes pain while increasing flexibility. As blood flow increases, so does the flow of oxygen and nutrients to the area while waste materials are removed.

Heat also works well for joint pain or as a pre-workout warm-up. Hot gel packs or heated water bottles work well for this and don’t pose any of the risks of electromagnetic field (EMF) exposure that most electric heating pads do.

Generally speaking, pain that is chronic and does not involve swelling will respond well to heat treatment. As with ice, you’ll want to use a barrier between the heat and your skin, such as a cloth. Apply the heat for 15 or 20 minutes at a time.

You may also want to try alternating heat and cold, which is a strategy often recommended by physical therapists and trainers. Apply heat for 20 minutes then follow immediately with 20 minutes of cold.

Related Coverage

For Faster Healing Use Heat, Not Ice

Another Way to Use Heat: Hyperthermic Conditioning

Heat-shock proteins (HSPs) are used by your cells to counteract potentially harmful stimulus. Whenever a cell is exposed to an unfriendly environment, the DNA separates in certain regions and begins to read the genetic code to produce these stress proteins.

HSPs are actually beneficial, helping to both prevent and repair damaged proteins. Heat-shock proteins are induced by heat, and this is one reason why sauna use is so beneficial.

According to Rhonda Perciavalle Patrick, Ph.D., increasing your core temperature for short periods, as is done by using a sauna, may offer dramatic improvements to your athletic performance.

Heat helps to soothe ongoing muscle aches and pains

She calls this concept “hyperthermic conditioning,” which emerging research suggests has multiple positive effects on your body, from increased endurance to the growth of new brain cells.

Hyperthemic conditioning, or “acclimating yourself to heat independent of aerobic physical activity through sauna use,” boosts endurance because it induces adaptations in your body that make it easier for you to perform when your body temperature is elevated.

In short, as your body is subjected to reasonable amounts of heat stress, it gradually becomes acclimated to the heat, prompting a number of beneficial changes to occur in your body.

The Benefits of Sauna Use

As your body adapts to heat stress, these adaptations include increased plasma volume and blood flow to your heart and muscles (which increase athletic endurance) along with increased muscle mass due to greater levels of heat-shock proteins and growth hormone.

In one study, those who had a 30-minute sauna session twice a week for three weeks after their workouts increased their time it took to run until exhaustion by more than 30 percent!

Daily sauna use has also been shown to cut men’s risk of death from fatal heart problems in half, compared to those who only used it once each week. Other physiologic adaptations that occur from hyperthermic conditioning include:

General Sauna Recommendations

Infrared saunas are known for their ability to promote detoxification, as discussed in a previous interview with Dr. Brian Clement, medical director of the Hippocrates Health Institute. By heating your tissues several inches deep, the infrared sauna can enhance your natural metabolic processes and blood circulation.

It also helps oxygenate your tissues. Your skin is a major organ of elimination, but many people do not sweat on a regular basis, thereby forgoing the benefits of this natural detoxification process. Repeated use of the sauna slowly restores skin elimination, which can help reduce your toxic load quite significantly. Many also enjoy saunas for relief of pain and muscle tension.

For all its health benefits, exposing your body to high temperatures should be done with commonsense and caution. If you’ve never taken a sauna before, start out by spending only a few minutes in there. Try a maximum of four minutes when first starting out.

Then, for each subsequent sauna, add about 30 seconds, and slowly work your way up to somewhere between 15 to 30 minutes. The reason for this is because the detoxification process can, in some cases, be severe, depending on your toxic load. General sauna recommendations are as follows:

  • Infrared sauna: 160-180 degrees Fahrenheit, for 15-30 minutes
  • Regular (Finnish wet or dry) sauna: 180-190 degrees Fahrenheit, for 10-20 minutes

Additionally, consider the following safety tips at all times:

When to Use Cold-Water Baths…

At the other end of the spectrum, exposing your body to cold temperatures may also have health benefits. For starters, intriguing research suggests heat-shock proteins may also be cold-induced.

In one animal study, cold exposure induced the expression of HSPs in brown fat, the implications of which are as yet unknown. It’s thought that cold-induced expression of heat-shock proteins may facilitate thermogenesis in beneficial brown fat, and, on a much broader scale, that exposing your body to reasonable amounts of both cold and heat stress may actually be beneficial.

Brown fat is a heat-generating type of fat that burns energy instead of storing it, and this may have important implications when it comes to weight loss. In one study, scientists found that they were able to activate brown fat in adult men by exposing them to cold temperatures. Swedish research published in 2009 also found that cold temperatures increased the activity in the subjects’ brown fat regions. In fact, cold-induced glucose uptake was increased by a factor of 15.

Based on animal models, researchers estimate that just 50 grams of brown fat (which is less than what most study volunteers have been found to have) could burn about 20 percent of your daily caloric intake—and more if “encouraged.”

Regular cold water and ice baths, otherwise known as cold-water immersion or “cryotherapy,” is also a popular technique among amateur and professional athletes, as it is thought to help reduce muscle inflammation and pain after exercise, as well as speed recovery time.

Indeed, after analyzing 17 trials involving over 360 people who either rested or immersed themselves in cold water after resistance training, cycling, or running, researchers found the cold-water baths were much more effective in relieving sore muscles one to four days after exercise.

Most studies on cold-water immersion report no or minimal side effects, so if you’re willing to spend 20 minutes or so in a cold tub of water, you may very well find some relief. Of course, common sense must be used. When you immerse yourself in cold water, it will shock your body to some degree, so you need to make sure the water is not too cold and you do not stay in it for too long.

Brief Exposure to Cold Water Might Promote ‘Hardening’

Exposing your whole body to cold water for short periods of time is also used to promote “hardening.” Hardening is the exposure to a natural stimulus, such as cold water, that results in increased tolerance to stress and/or disease. This was demonstrated by a study involving 10 healthy people who swam regularly in ice-cold water during the winter. Following exposure to the cold water, researchers noted:

  • “Drastic” decrease in uric acid levels: High levels of uric acid are normally associated with gout, but it has been long known that people with high blood pressure, kidney disease, and people who are overweight often have elevated uric acid levels. When your uric acid level exceeds about 5.5 mg per deciliter, you have an increased risk for a host of diseases including heart disease, fatty liver, obesity, diabetes, hypertension, kidney disease, and more.
  • Increase in glutathione: Glutathione is your body’s most powerful antioxidant, which keeps all other antioxidants performing at peak levels.

Personally, I have been experimenting with cold-water immersion for a couple of years. I will go into the shower without allowing it to warm up, and I also go in the ocean without a wet suit on when most people consider it too cold to swim. I have found that if I hold my breath it really helps adjust to the initial shock, and I rapidly acclimate to the cold. I have come to enjoy it and now view it as a form of healthy stress, very similar to exercise.

Cold therapy works well after a sudden injury,

If you decide to give any type of cold-water immersion a try, be sure to listen to your body and work up to the more advanced techniques gradually. There are a number of different options you can try:

  • Place an ice pack on your upper back and upper chest for 30 minutes per day (you can do this while relaxing in front of the TV for example)
  • Drink about 500 ml of ice water each morning
  • Take cold showers
  • Immerse yourself in ice water up to your waist for 10 minutes, three times per week. (Simply fill your tub with cold water and ice cubes)

And remember, you can use hot and cold therapeutically for muscle and joint pain and injuries, respectively. If you have swelling and an acute injury, apply cold using an ice or gel pack for 20 minutes at a time. For chronic aches and pains, use a gel pack or hot water bottle for 20 minutes for relief.

Exposure to Sun, Heat and Humidity Can Exacerbate Symptoms of Mental Disorders

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Summary: Researchers report exposure to hot, humid weather can trigger mental health symptoms that require emergency care.

Source: University at Albany

Exposure to sunny, hot and humid weather can trigger severe symptoms of mental disorders, requiring emergency care. So reports a recent study, led by researchers at the University at Albany, which used data on New York State weather and hospital emergency visits to assess how features of summer weather affect people with mental disorders.

The research was the first to evaluate combined effects of multiple meteorological factors across all classes of mental disorders designated by the World Health Organization.

These findings, published in Environment International, could inform strategies to improve patient care.

Lead author Xinlei Deng, who completed his Ph.D. in May in the Department of Environmental Health Sciences at UAlbany, says, “We know that weather affects mood. But while a warm, bright day is a boost for some, others can become more easily agitated or quicker to anger. For people with mental disorders, changes in multiple weather factors can provoke symptoms that pose serious health risks.”

“By examining local weather conditions together with information on emergency department visits, we found clear trends connecting high heat, humidity and sun exposure with increased emergency admissions due to mental disorders, especially among patients suffering symptoms linked to psychoactive substance use, mood disorders, stress disorders and adult behavior disorders, which can include forms of violence like pyromania.

” Understanding these connections can help care providers shape interventions to protect patient well-being.”

The statewide analysis included two six-month study periods, focusing on the warmer months: May-October, in 2017 and 2018.

The team leveraged meteorological data from NYS Mesonet––a UAlbany-operated network of 126 weather stations in every county and borough in New York, which record atmospheric and soil conditions at 5-minute intervals. Their study looked at data on temperature, solar radiation, relative humidity, heat index and rainfall.

Emergency department visits due to mental disorders were identified using the International Classification of Diseases (ICD-10). Disorders are coded by subtype, which include categories like stress-related disorders, intellectual disabilities and intentional self-harm.

Over the study periods, 547,540 emergency department visits attributed to mental disorders were recorded in New York State. To link local weather conditions and emergency department visits, the residential address of each case was geocoded and paired with the nearest Mesonet station. Information on patient diagnoses and demographics was obtained from the New York Statewide Planning and Research Cooperative System, a mandatory hospital discharge database covering ~95% of hospitals in the state.

Results showed that the combination of high temperature, solar radiation and relative humidity posed the greatest risk of severe mental disorder symptoms. Effects were strongest in the summer transition months of September and October. Populations impacted most acutely included: males, Hispanic and African American individuals, people aged 46-65, Medicaid or Medicare subscribers, and people without insurance.

Several mental disorder classes were distinctly responsive to certain combinations of weather conditions. For example, hospitals saw increased emergency department visits due to psychoactive substance use (e.g., consuming alcohol or opioids) when solar radiation, temperature, heat index and humidity were high.

Severe symptoms of mood disorders, which include depression and bipolar disorders, coincided with less sun and high heat.

“As extreme heat becomes increasingly intense and more frequent due to climate change, we can expect these changes to have adverse physiological effects on people,” said Shao Lin, senior author of the study and a professor at UAlbany’s School of Public Health.

“Individuals with mental disorders are especially vulnerable to these changes, and our findings suggest that multiple, simultaneous weather stressors may compound health risk. Efforts to hone targeted care must take combined factors into account.”

This shows an overheated man on a beach
Exposure to sunny, hot and humid weather can trigger severe symptoms of mental disorders, requiring emergency care.

Since mental health symptoms associated with weather can take time to manifest, the team measured “lag days” –– time between the onset of a particular weather condition and the date of hospital admittance –– to account for this delay. They found that high temperature alone presented the most immediate short-term risk, while heat index increased risk over a two-week period.

Deng, now doing postdoctoral work at the National Institutes of Health, explains, “As we learn more about the ways that weather affects mental health, putting a finer point on symptom emergence timing is critical.

Understanding lag effects could help hospital caregivers know when to prepare to receive a higher number of patients in the wake of prolonged weather conditions known to exacerbate certain mental disorders.”

Public health agencies like the CDC could use these findings to establish early-warning systems to preempt mental health-related violence and syndromes. Proactive measures could include facilitating access to cooling centers and encouraging patients with relevant mental disorders to pay attention to heatwaves and sun exposure, and take shelter as appropriate.

“Knowing that transition months see the highest risk of severe symptoms tells us that early warning systems and related education should start in May and continue through September-October,” Lin said. “Policymakers can plan preparedness efforts using health risk thresholds connected to weather factors.”

“Weather and climate have profound impacts on health –– directly from severe and hazardous weather to more indirect impacts from allergens and mental health,” said Jerry Brotzge, a coauthor of the paper and the New York State Mesonet’s long-time program manager who was recently hired as state climatologist in his home state of Kentucky.

“Recent advances in weather observations collected at high temporal and spatial scales, like those recorded by Mesonet, have the potential to revolutionize our understanding of how changes in weather cause changes in health. Once we understand these relationships better, we can respond to patients’ needs more effectively.”

Abstract

Identifying joint impacts of sun radiation, temperature, humidity, and rain duration on triggering mental disorders using a high-resolution weather monitoring system

Background

Mental disorders (MDs) are behavioral or mental patterns that cause significant distress or impairment of personal functioning. Previously, temperature has been linked to MDs, but most studies suffered from exposure misclassification due to limited monitoring sites. We aimed to assess whether multiple meteorological factors could jointly trigger MD-related emergency department (ED) visits in warm season, using a highly dense weather monitoring system.

Methods

We conducted a time-stratified, case-crossover study. MDs-related ED visits (primary diagnosis) from May-October 2017–2018 were obtained from New York State (NYS) discharge database. We obtained solar radiation (SR), relative humidity (RH), temperature, heat index (HI), and rainfall from Mesonet, a real-time monitoring system spaced about 17 miles (126 stations) across NYS. We used conditional logistic regression to assess the weather-MD associations.

Results

For each interquartile range (IQR) increase, both SR (excess risk (ER): 4.9%, 95% CI: 3.2–6.7%) and RH (ER: 4.0%, 95% CI: 2.6–5.4%) showed the largest risk for MD-related ED visits at lag 0–9 days. While temperature presented a short-term risk (highest ER at lag 0–2 days: 3.7%, 95% CI: 2.5–4.9%), HI increased risk over a two-week period (ER range: 3.7–4.5%), and rainfall hours showed an inverse association with MDs (ER: −0.5%, 95% CI: 0.9-(-0.1)%). Additionally, we observed stronger association of SR, RH, temperature, and HI in September and October. Combination of high SR, RH, and temperature displayed the largest increase in MDs (ER: 7.49%, 95% CI: 3.95–11.15%). The weather-MD association was stronger for psychoactive substance usage, mood disorders, adult behavior disorders, males, Hispanics, African Americans, individuals aged 46–65, or Medicare patients.

Conclusions

Hot and humid weather, especially the joint effect of high sun radiation, temperature and relative humidity showed the highest risk of MD diseases. We found stronger weather-MD associations in summer transitional months, males, and minority groups. These findings also need further confirmation.

How Does the Brain Process Heat as Pain?

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Summary: Researchers have uncovered a neural circuit that involves spinal neurons and a signaling pathway that is responsible for how burning pain is sensed.

Source: Case Western Reserve

The world has changed since 1664, when French philosopher and scientist Rene Descartes first claimed the brain was responsible for feeling the sensation of pain.

However, a key question remains: How exactly does the human brain feel pain? Specifically, thermal pain—like that experienced when touching an open flame or a hot pan while cooking.

A team of researchers in the neurosciences department at the Case Western Reserve University School of Medicine think they’ve found an answer—that a neural circuit involving spinal neurons and a signaling pathway––are responsible for how burning pain is sensed.

They believe their discovery, published recently in the journal Neuron, could lead to more effective treatment for chronic, pathological pain—such as shooting, stabbing and burning pain—because it may involve the same signaling pathway.

“We know that heat, cold, pressure and itching stimulations to our skin result in appropriate feelings in the brain. However, the neurons encoding the heat signals in the spinal cord were unclear,” said Hongsheng Wang, study lead author and a postdoctoral fellow at the School of Medicine.

“Our study identified a group of interneurons in the spinal cord required for heat sensation. We also found a signaling pathway contributes to heat hypersensitivity caused by inflammation or nerve injuries.”

The study

The brain controls everything we do, from our perception of the world around us to how we move our bodies and experience sensations. The process involves neurons, which are cells that act as messengers to transmit information between the brain and nervous system. The neurons send information through complex circuits throughout the body.

The research team looked at neurons in the spinal cord and their role in thermal pain by analyzing mouse models and their response to heated plates. During this process, the team identified the activation of a “novel,” or newly discovered, class of spinal cord neurons (called ErbB4+) that process heat signals to the spinal cord.

The team wanted to look further into whether these neurons specifically are responsible for thermal pain. There are several ways to test this, including destroying the ErbB4+ neurons.

This shows a diagram from the study
The brain controls everything we do, from our perception of the world around us to how we move our bodies and experience sensations. Credit: The Researcher

The researchers expressed a toxin specifically targeting the ErbB4+ neurons. Once the neurons were destroyed, the response to heat pain was impaired. This demonstrated that ErbB4+ neurons are specifically tied to how thermal pain is sensed and, when destroyed, pain is not felt less.

They also examined the role of neuregulin 1 (NRG1), a protein involved in many cellular functions. They found that NRG1 and its receptor tyrosine kinase ErbB4 (often referred to as the NRG1 signaling) is also involved in the sensation of thermal pain.

The findings

“Pain is a sensation we have all experienced. For most of us, pain is temporary,” said Lin Mei, professor and chair of the Department of Neurosciences at the School of Medicine and study corresponding author.

“However, for patients with pathological pain, the pain experience is unending, with little hope for relief. Scientists have long believed it’s a result of dysfunctional neuronal activity.”

Mei said their study showed that pathological pain can be reduced by injecting an ErbB4+ inhibitor or an NRG1 neutralizing peptide.

The application of these discoveries may go beyond the therapeutic treatment of pathological pain.

“Both NRG1 and ErbB4 are risk genes of many brain disorders including major depression and schizophrenia,” Mei said.

“Further studies are warranted to show if the mechanism of heat pain and pathological pain also plays a role in different types of pain experienced by those who have brain disorders.”

Abstract

A novel spinal neuron connection for heat sensation

Highlights

  • Spinal ErbB4+ neurons are activated by heat and synapsed by TRPV1+ nociceptors
  • Heat sensation is reduced by ErbB4+ neuron ablation or inhibition
  • Augmented effect on heat sensation by inhibiting ErbB4+, SST+, and CCK+ neurons together
  • NRG1-ErbB4 signaling promotes heat sensation and hypersensitivity

Summary

Heat perception enables acute avoidance responses to prevent tissue damage and maintain body thermal homeostasis. Unlike other modalities, how heat signals are processed in the spinal cord remains unclear.

By single-cell gene profiling, we identified ErbB4, a transmembrane tyrosine kinase, as a novel marker of heat-sensitive spinal neurons in mice. Ablating spinal ErbB4+ neurons attenuates heat sensation.

These neurons receive monosynaptic inputs from TRPV1+ nociceptors and form excitatory synapses onto target neurons. Activation of ErbB4+ neurons enhances the heat response, while inhibition reduces the heat response.

We showed that heat sensation is regulated by NRG1, an activator of ErbB4, and it involves dynamic activity of the tyrosine kinase that promotes glutamatergic transmission.

Evidence indicates that the NRG1-ErbB4 signaling is also engaged in hypersensitivity of pathological pain.

Together, these results identify a spinal neuron connection consisting of ErbB4+ neurons for heat sensation and reveal a regulatory mechanism by the NRG1-ErbB4 signaling.

Physicists have found a metal that conducts electricity but not heat

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Defying one of the most fundamental laws of conductors.

Researchers have identified a metal that conducts electricity without conducting heat – an incredibly useful property that defies our current understanding of how conductors work.

The metal contradicts something called the Wiedemann-Franz Law, which basically states that good conductors of electricity will also be proportionally good conductors of heat, which is why things like motors and appliances get so hot when you use them regularly.

 But a team in the US has shown that this isn’t the case for metallic vanadium dioxide (VO2) – a material that’s already well known for its strange ability to switch from a see-through insulator to a conductive metal at the temperature of 67 degrees Celsius (152 degrees Fahrenheit).

“This was a totally unexpected finding,” said lead researcher Junqiao Wu, from Berkeley Lab’s Materials Sciences Division.

“It shows a drastic breakdown of a textbook law that has been known to be robust for conventional conductors. This discovery is of fundamental importance for understanding the basic electronic behaviour of novel conductors.”

Not only does this unexpected property change what we know about conductors, it could also be incredibly useful – the metal could one day be used to convert wasted heat from engines and appliances back into electricity, or even create better window coverings that keep buildings cool.

Researchers already know of a handful of other materials that conduct electricity better than heat, but they only display those properties at temperatures hundreds of degrees below zero, which makes them highly impractical for any real-world applications.

Vanadium dioxide, on the other hand, is usually only a conductor at warm temperatures well above room temperature, which means it has the ability to be a lot more practical.

 To uncover this bizarre new property, the team looked at the way that electrons move within vanadium dioxide’s crystal lattice, as well as how much heat was being generated.

Surprisingly, they found that the thermal conductivity that could be attributed to the electrons in the material was 10 times smaller than that amount predicted by the Wiedemann-Franz Law.

The reason for this appears to be the synchronised way that the electrons move through the material.

“The electrons were moving in unison with each other, much like a fluid, instead of as individual particles like in normal metals,” said Wu.

“For electrons, heat is a random motion. Normal metals transport heat efficiently because there are so many different possible microscopic configurations that the individual electrons can jump between.”

“In contrast, the coordinated, marching-band-like motion of electrons in vanadium dioxide is detrimental to heat transfer as there are fewer configurations available for the electrons to hop randomly between,” he added.

Interestingly, when the researchers mixed the vanadium dioxide with other materials, they could ‘tune’ the amount of both electricity and heat that it could conduct – which could be incredibly useful for future applications.

For example, when the researchers added the metal tungsten to vanadium dioxide, they lowered the temperature at which the material became metallic, and also made it a better heat conductor.

That means that vanadium dioxide could help dissipate heat from a system, by only conducting heat when it hits a certain temperature. Before that it would be an insulator.

Vanadium dioxide also has the unique ability of being transparent to around 30 degrees Celsius (86 degrees Fahrenheit), but then reflects infrared light above 60 degrees Celsius (140 degrees Fahrenheit) while remaining transparent to visible light.

So that means it could even be used as a window coating that reduces the temperature without the need for air conditioning.

“This material could be used to help stabilise temperature,” said one of the researchers, Fan Yang.

“By tuning its thermal conductivity, the material can efficiently and automatically dissipate heat in the hot summer because it will have high thermal conductivity, but prevent heat loss in the cold winter because of its low thermal conductivity at lower temperatures.”

A lot more research needs to be done on this puzzling material before it’s commercialised further, but it’s pretty exciting that we now know these bizarre properties exist in a material at room temperature.

How much heat can the human body possibly take?

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How far can you push the human body before it fails? The New Scientist posed that question a few years ago, listing out a few “ultimate limits” for the human body: how fast can we run, how long can we concentrate, how long can we survive without sleep and so on. The one question they did not ask, and that’s increasingly bothering us, is: how much heat can we tolerate before we perish?

It’s just May. And we are already battling an intense heat wave. Last year, NASA experts predicted that in 2015, planet Earth will face an unprecedented heat wave. The three decades from 1983 to 2012 have been the warmest in the last 1,400 years. And summer of 2015 will be excruciatingly hot in several parts of the world. Clearly, India is one of those.

What’s excruciatingly hot for us? Remember 2010, when temperature hit a 50-year-high with Jalgaon in Maharashtra crossing 49 degrees? No. India has seen more: the highest so far has been 50.6 degrees at Alwar, Rajasthan, in May 1956.

Apparently, that’s not enough to make us one of the most spectacular hotspots in the world. At least, we haven’t seen temperature going up to 71 degrees, as it did at the salt deserts of Dasht-e Lut, Iran, in 2005. Or 69.3 degrees as in Queensland, Australia, in 2003. Or even neighbour Pakistan’s 2010 record, when temperature soared to 53.7 degrees at Mohenjo-daro — one of the warmest temperatures ever recorded in the world.

So how much heat can you tolerate? As much as your genes allow. Heat tolerance is coded in your genes. The mechanism goes back to human evolution over 1.7 million years, when humans started coming out of forested areas into open grassy lands. To survive the heat and to keep cool, our ancestors started losing body hair. A genetic adaptation for survival — just as bipedalism, a prominent nose, a large brain, and the ability to speak are. There’s more: people who are tall, slim and slender tolerate heat better. They have more skin to perspire. Woe be unto those who are fat: they have less skin surface for their weight.

Generally, the range between 18 degrees and 24 degrees is best for the body, says the World Health Organisation (WHO). But when temperature nears 40 degrees, the body finds it difficult to cool down — with or without humidity — leading to heat cramps, exhaustion, breathing difficulty and increased heart rate. If mercury soars well above 40 degrees, the heat can cause permanent damage to vital organs. As we all know, heat can be a killer.

Well, there’s a caveat from WHO: Your heat tolerance is linked to what you are used to. So Dilliwalas would fare better, than say Londoners, if the mercury goes beyond reasonable limits. Simply because we are used to it.

Some consolation that.