You know it’s hot when summer camps have to cancel bonfires and doctors warn that playgrounds could be dangerous. Last week, when a heat dome was descending on New York City, I grew a bit concerned myself. My children’s outdoor day camp promised to “pivot to ‘water games,’” as the email put it, and said that there would be fans and misters. “Of course,” the camp added, “if you feel the heat for the rest of this week will not set your camper up for success, feel free to keep them at home.”
And why not? The public-health advice is pretty clear on just this point: Kids are not, in fact, well equipped for scorching weather. “Children are especially at risk of heat-related illnesses,” says heat.gov, a website run by a collaboration of the CDC, the National Oceanic and Atmospheric Administration, and many other federal agencies. Essentially the same message is repeated almost everywhere a mom or dad might go for guidance: in academic articles and UNICEF announcements, in messaging from the EPA and state public-health departments, in published interviews with specialists in pediatric medicine.
The weird thing is, actual heat-related-illness data seem to tell a different story—that kids are unusually resilient when it comes to heat. Take heat-related deaths: According to a large-scale study from the CDC, the lowest rate applied to those ages 5 to 14. The same pattern largely holds for heat-related hospitalizations and visits to the emergency room, at least in the United States: Children tend to have the lowest risk.
For a parent who wants to know whether his feisty 7-year-old will be safe at camp when it’s 99 degrees, this disparity between the standard public-health advice and the epidemiological evidence is baffling. I just want to know: Is my camper set up for success, or isn’t he?
This turns out to be a parable about the long and winding road that runs from mere hypotheses through lab results and real-world data, and then on to solid truth. The scientific thinking that produced the standard, blanket warnings about overheated kids is almost 50 years old. Its reasoning is sound. But decades’ worth of research has since produced a bunch of unexpected findings, and some aspects of the old idea have had to be adjusted—if not completely overturned.
In 1980, the founding father of pediatric exercise medicine, the Canadian Israeli physician Oded Bar-Or, laid out the case that kids might be uniquely vulnerable to overheating. His paper “Climate and the Exercising Child” noted that, for one thing, children’s bodies have more surface area relative to body mass than adults’. At mild or warm temperatures, this helps them cool off more quickly, as heat dissipates from their skin into surrounding air. But when the weather gets extremely hot—hotter than the surface of our skin, which might be 94 or 95 degrees—this process would be expected to reverse: At that point, children’s greater surface area ought to make them take on heat more quickly than adults. Bar-Or also pointed out that children have a smaller sweat response than adults at the same temperatures, and he suggested that kids may acclimatize to heat more slowly. Shortly thereafter, in the summer of 1982, the American Academy of Pediatrics (AAP) put out its first official warning on the matter. This message has persisted, more or less, until today.
In the meantime, though, the underlying science has shifted. One of Bar-Or’s former graduate students, Bareket Falk, told me that in the ’90s, the lab gathered data suggesting that even when children were subjected to triple-digit temperatures, they seemed to fare no worse than adolescents or adults at maintaining their body temperature. Other research pointed in the same direction, and by 2008, Falk and other exercise physiologists were arguing against the status-quo assumption that kids had some major natural deficits in thermoregulation.
More recent work has only reinforced the changing view. “There’s been quite a reversal of the thinking,” Caroline J. Smith, the director of the Environmental & Occupational Physiology Laboratory at Appalachian State University, told me. Sure, children produce less sweat than adults do—but their sweating may be more efficient. “They actually have less electrolytes in their sweat, so it evaporates a little more easily,” she said. (The evaporation of sweat is what cools the body.) Falk, who is now a professor of kinesiology at Brock University, said that kids’ sweat forms in smaller droplets, which may also help the sweat evaporate, and that kids don’t tend to waste their sweat as grown-ups do, by pouring out so much that it soaks their T-shirts and drips off onto the ground. The AAP changed its policy in 2011, noting that the facts had changed: Kids are not, in fact, especially vulnerable to heat, it said.
But as before, the thinking on this question ran a little faster than the evidence. Even now, researchers have barely any data showing heat’s effects on young children, who are more challenging to study in the lab. “There’s a lack of knowledge, despite what you may have read,” Glen Kenny, the director of the Human and Environmental Physiology Research Unit at the University of Ottawa, told me. “There are studies that have been essentially designed incorrectly.” In his view, more and better research must be done, and until that happens, the old assumptions are still basically correct: “Do we know that children are more vulnerable? Yeah, because it comes down to both a combination of size and the development of the heat-loss mechanisms, your ability to sweat and your ability to increase blood flow.” He also said that short-term lab experiments tell you nothing of the pernicious, longer-term effects of overheating: Being hot for many hours, or many days, may affect a child’s body, degrade his mood, or hamper school performance.
So why don’t we see more cases of pediatric heat-related illness, if children are at elevated risk? Kenny said that it’s because children are looked after by adults. An elderly person, living alone, might succumb to heat exhaustion with no one around to help; a kid who ends up overheated at a summer camp will be tended to by counselors. In other words, kids may be physiologically more vulnerable and behaviorally at risk, just as the standard public-health advice suggests—but they’re socially protected. The stats might also miss lesser forms of heat-related illness, Perry Sheffield, a pediatrician and an environmental-health researcher at the Icahn School of Medicine at Mount Sinai, told me. “You know, if a child gets a little bit dehydrated and then throws up all night, then you’re not sending them to camp the next day,” she said.
At least for kids below the age of 10, defaulting to the old precautions may be reasonable, Smith said. In any case, the same principles of mitigating risk—staying hydrated, avoiding exercise during the hottest parts of the day, seeking shade, acclimating to the weather, wearing loose-fitting clothes—apply to young and old alike.
Still, if everyone should take precautions against the heat, what is really gained by saying that kids are at extra-special risk? Those who prefer this cautious guidance might say that no harm is done. But people do react dramatically to the idea that kids might be in danger. In the United Kingdom, more than 1,000 schools closed during last month’s record-setting European heat wave, and those choices naturally brought up memories of pandemic policies, and old debates over how such restrictions should be understood. Are the school officials following the science, or are they succumbing to alarmist tendencies in public health? Speaking as a parent, I wish there were a simple answer to that question.
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