What a Heat Wave Does to Your Body. The human body is a remarkably effective cooling machine—but it has a limit. By Dhruv Khullar  Deadly heat, once rare, is spreading. This summer—which is likely to be the hottest in recorded history—Beijing warmed to a hundred and six degrees and Sardinia baked at a hundred and eighteen. For forty-four consecutive days, El Paso recorded temperatures of a hundred or more. We’re all becoming guinea pigs in a vast experiment: How will people of different ages and levels of fitness respond to unprecedented, ongoing heat? What will happen to our bodies when we have no choice but to stay outside, or when the air-conditioning goes out?  Deadly heat, once rare, is spreading. This summer—which is likely to be the hottestin recorded history—Beijing warmed to a hundred and six degrees and Sardinia baked at a hundred and eighteen. For forty-four consecutive days, El Paso recorded temperatures of a hundred or more. We’re all becoming guinea p gs in a vast experiment: How will people of different ages and levels of fitness respond to unprecedented, ongoing heat? What will happen to our bodies when we have no choice but to stay outside, or when the air-conditioning goes out?  The human body is astonishingly good at cooling itself off. The hypothalamus, an almond-size structure deep inside the brain, responds to heat by stimulating sweat production. It also speeds up the heart, dilates blood vessels, and shunts blood to the extremities. The basic principle is to get hot blood near the skin, where heat can dissipate in a number of ways. When air currents wash over us, it can leave through convection. Heat can be lost directly, through radiation, in the form of electromagnetic waves. Most importantly, as we sweat, evaporation cools our skin. The problem with extreme heat is that it makes the first three mechanisms less effective, or even turns them into routes for gaining heat. When humidity rises, the fourth mechanism weakens, too.                                                                                Heat affects us on a molecular level. Excess heat interferes with the chemical bonds that help proteins to twist and fold into shape; just as a hot frying pan can denature the proteins in an egg, high body temperatures can denature the proteins in our cells, preventing them from functioning properly and even killing them off, especially in the liver, blood vessels, and brain. On the scale of the whole body, meanwhile, overheating can trigger a downward spiral. Sweating can leave a person dehydrated; this, in turn, means that there’s less liquid available to carry heat away. Desperate to release heat, the body diverts more blood to its periphery, starving internal organs of oxygen and nutrients. In very bad cases of heat illness, the gut can lose its integrity, allowing deadly bacteria to leach into the bloodstream, or the heat can set off a frenzy of inflammation known as a cytokine storm. In the most severe heat, the body’s enzymes—the proteins that carry out life’s essential chemical reactions—cease to function. Doctors divide heat strokes into two categories. Classic heat stroke generally occurs at rest, and is more common among kids, older people, and those with chronic conditions. Exertional heat stroke strikes athletes, laborers, soldiers, and others engaged in strenuous activity. To avoid both kinds of illness, our bodies adjust. This fundamental defense against heat exists in virtually every species on earth. Over time—on a scale of days or weeks—our bodies can adjust to extreme heat. They learn to increase the amount of blood that circulates and pump it toward the skin more efficiently. Our bodies start to sweat more and at lower temperatures, and we get better at holding on to our electrolytes instead of sweating them away. Yet acclimation takes time—and this is one reason heat waves tend to be deadliest at their start, especially in places where people aren’t used to hot weather. (Last summer, temperatures as high as a hundred and four degrees were thought to have contributed to as many as eleven thousand deaths in France.) Unfortunately, the adaptation process reverses shortly after we return to normal temperatures. Last summer won’t help you much with this one. There is an increased risk of post-traumatic stress disorder after many serious illnesses, but heat in particular has been linked to an array of mental-health problems. Hotter days are associated with anxiety, anger, irritability, disordered sleep, and violent crime; as temperatures rise, so do suicide attempts and overdose deaths. In its 2022 report, the Intergovernmental Panel on Climate Change said, with high confidence, that the warming planet is adversely affecting people’s mental well-being. Heat illness is only one of the physical ailments caused by heat waves......There is an increased risk of post-traumatic stress disorder after many serious illnesses, but heat in particular has been linked to an array of mental-health problems. Hotter days are associated with anxiety, anger, irritability, disordered sleep, and violent crime; as temperatures rise, so do suicide attempts and overdose deaths. .....there's much more so read on          https://link.newyorker.com/view/5e2bb2c62a077c05ea0a9723jcwap.15d0u/9115d9fe