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The feature was removed on select smartwatches due to a patent-infringement lawsuit, but Apple has “redesigned” it.

Nature, Published online: 13 June 2025; doi:10.1038/d41586-025-01862-xEarth’s magnetic field seems to correlate with conditions that helped complex life to thrive — a discovery that could aid the search for life on distant exoplanets.

The nightmare was real, the situation was not.Revenge of the Savage Planet, an adventure spread across a number of distant — and quite savage! — planets, invites nonlinear exploration. To complete its missions and discover all of its secrets, you must leap into an unknown where the otherworldly flora, fauna, and even the inorganic material are primed to kill you. So, shortly after assembling an underwater scooter that allowed my robot sidekick to whisk me through the depths of alien oceans, I descended into a series of caverns under the Zenithian Rift to see what was going on down there. The specters of death I encountered below weren’t even designed to haunt me.In Raccoon Logic’s sequel to Journey to the Savage Planet, players are tasked with scanning every object in every nook and cranny to assemble an exhaustive log of materials located on each planet. At first, the task is a walk in the (overgrown killer) park: find a tree, scan a tree. Find a slobbering beastie, scan a slobbering beastie. But a counter on the map charting your scannables becomes the most daunting subtask — can I really find every single micro scannable? I found myself longing after completing the core missions. To really 100% this, there was even more reason to venture into the most uninviting spaces, including a dark underwater cave on Zenithian Rift that absolutely did not look like it contained any scannable items. But I couldn’t not go in there.It took about two seconds for me to realize… I had made a horrible mistake. While the cave was easily accessible from the water, there were no enemy or collectible breadcrumbs to suggest this was a place the folks at Raccoon Logic intended for me to. I was lured in by curiosity, but the joy of discovery in Revenge of the Savage Planet got the best of me. Now I was stuck. I had stumbled into a graphical anomaly, an in-game black hole that had an entrance but no apparent exit. In Revenge of the Savage Planet, you can’t beam back to starting locations on the fly or off yourself in order to respawn from your last save. In a clever but likely divisive design choice, the game forces you to navigate to transporters spread across the worlds in order to beam off to your next desired location, which forces traversal and new encounters. But it meant that while bumbling around in the dark, hoping to find a way out of my watery grave, I couldn’t simply die and move on. I was actually trapped, and in a scenario I haven’t experienced in quite some time, feeling IRL like I was actually trapped.I already don’t do well with underwater levels out of an intense fear of drowning. Luckily for me, most games will throw me the lifeline of a visual countdown to illustrate oxygen levels, ensuring (1) I surface in time and (2) I don’t hyperventilate over the stress of surfacing in time. Revenge of the Savage Planet doesn’t need that because there’s no punishment for enjoying the waters; you’re already in a spacesuit and the challenges you encounter via underwater scooter require a bunch of time-intensive back and forth. Doing it all on limited air would simply not be fun. But that meant, stuck in this tight underwater cave, I would never die. I was in limbo. Or maybe I was in hell.I spent far too long searching for a route out. Streaks of light bled in from a theoretical escape that I could never reach — any time I thought I was close, I bumped into a new rock and found myself jetting in the opposite direction. Not since I watched The Rescue, the riveting-yet-terrifying documentary about the team of divers who squeezed through cave passageways to free 12 trapped Thai soccer players, had my apparent claustrophobia had its way with my nerves. I can’t quite explain why I pushed myself over the edge to find an in-game solution to this unintentional challenge, except to say that I really wanted to do a good job at Revenge of the Savage Planet.Most glitches are considered errors by programmers, annoyances by players, and occasionally shortcuts for the speedrunner crowd. Revenge of the Savage Planet’s death cave might fall into the first two categories, but it’s a harrowing experience I ultimately appreciated, a unique screw up that could only happen in a game. I have never felt truly trapped in a film, despite the best efforts of 3D stereoscopic effects and 4DX rumble seats. After finally rebooting Revenge of the Savage Planet, I had to give myself a few minutes to let my heart rate die down before I grabbed the controller. But I got right back to it. Sure, this was a glitch, but in a game where exploration is everything, leaping into a true unknown — one that the creators of the game clearly didn’t intend me to find — was its own form of success.Revenge of the Savage Planet is currently available for PC, Playstation, and Xbox, and it’s currently on Game Pass.See More:

June 3, 20255 min readAre We Ready for Death in Space?NASA has quietly taken steps to prepare for a death in space. We need to ask how nations will deal with this inevitability now, as more people start traveling off the planetBy Peter Cummings edited by Lee Billings SciePro/Science Photo Library/Getty ImagesIn 2012 NASA stealthily slipped a morgue into orbit.No press release. No fanfare. Just a sealed, soft-sided pouch tucked in a cargo shipment to the International Space Station (ISS) alongside freeze-dried meals and scientific gear. Officially, it was called the Human Remains Containment Unit (HRCU). To the untrained eye it looked like a shipping bag for frozen cargo. But to NASA it marked something far more sobering: a major advance in preparing for death beyond Earth.As a kid, I obsessed over how astronauts went to the bathroom in zero gravity. Now, decades later, as a forensic pathologist and a perennial applicant to NASA’s astronaut corps, I find myself fixated on a darker, more haunting question:On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.What would happen if an astronaut died out there? Would they be brought home, or would they be left behind? If they expired on some other world, would that be their final resting place? If they passed away on a spacecraft or space station, would their remains be cast off into orbit—or sent on an escape-velocity voyage to the interstellar void?NASA, it turns out, has begun working out most of these answers. And none too soon. Because the question itself is no longer if someone will die in space—but when.A Graying CorpsNo astronaut has ever died of natural causes off-world. In 1971 the three-man crew of the Soviet Soyuz 11 mission asphyxiated in space when their spacecraft depressurized shortly before its automated atmospheric reentry—but their deaths were only discovered once the spacecraft landed on Earth. Similarly, every U.S. spaceflight fatality to date has occurred within Earth’s atmosphere—under gravity, oxygen and a clear national jurisdiction. That matters, because it means every spaceflight mortality has played out in familiar territory.But planned missions are getting longer, with destinations beyond low-Earth orbit. And NASA’s astronaut corps is getting older. The average age now hovers around 50—an age bracket where natural death becomes statistically relevant, even for clean-living fitness buffs. Death in space is no longer a thought experiment. It’s a probability curve—and NASA knows it.In response, the agency is making subtle but decisive moves. The most recent astronaut selection cycle was extended—not only to boost intake but also to attract younger crew members capable of handling future long-duration missions.NASA’s Space MorgueIf someone were to die aboard the ISS today, their body would be placed in the HRCU, which would then be sealed and secured in a nonpressurized area to await eventual return to Earth.The HRCU itself is a modified version of a military-grade body bag designed to store human remains in hazardous environments. It integrates with refrigeration systems already aboard the ISS to slow decomposition and includes odor-control filters and moisture-absorbent linings, as well as reversed zippers for respectful access at the head. There are straps to secure the body in a seat for return, and patches for name tags and national flags.Cadaver tests conducted in 2019 at Sam Houston State University have proved the system durable. Some versions held for over 40 days before decomposition breached the barrier. NASA even drop-tested the bag from 19 feet to simulate a hard landing.But it’s never been used in space. And since no one yet knows how a body decomposes in true microgravity (or, for that matter, on the moon), no one can really say whether the HRCU would preserve tissue well enough for a forensic autopsy.This is a troubling knowledge gap, because in space, a death isn’t just a tragic loss—it’s also a vital data point. Was an astronaut’s demise from a fluke of their physiology, or an unavoidable stroke of cosmic bad luck—or was it instead a consequence of flaws in a space habitat’s myriad systems that might be found and fixed? Future lives may depend on understanding what went wrong, via a proper postmortem investigation.But there’s no medical examiner in orbit. So NASA trains its crews in something called the In-Mission Forensic Sample Collection protocol. The space agency’s astronauts may avoid talking about it, but they all have it memorized: Document everything, ideally with real-time guidance from NASA flight surgeons. Photograph the body. Collect blood and vitreous fluid, as well as hair and tissue samples. Only then can the remains be stowed in the HRCU.NASA has also prepared for death outside the station—on spacewalks, the moon or deep space missions. If a crew member perishes in vacuum but their remains are retrieved, the body is wrapped in a specially designed space shroud.The goal isn’t just a technical matter of preventing contamination. It’s psychological, too, as a way of preserving dignity. Of all the “firsts” any space agency hopes to achieve, the first-ever human corpse drifting into frame on a satellite feed is not among them.If a burial must occur—in lunar regolith or by jettisoning into solar orbit—the body will be dutifully tracked and cataloged, treated forevermore as a hallowed artifact of space history.Such gestures are also of relevance to NASA’s plans for off-world mourning; grief and memorial protocols are now part of official crew training. If a death occurs, surviving astronauts are tasked with holding a simple ceremony to honor the fallen—then to move on with their mission.Uncharted RealmsSo far we’ve only covered the “easy” questions. NASA and others are still grappling with harder ones.Consider the issue of authority over a death and mortal remains. On the ISS, it’s simple: the deceased astronaut’s home country retains jurisdiction. But that clarity fades as destinations grow more distant and the voyages more diverse: What really happens on space-agency missions to the moon, or to Mars? How might rules change for commercial or multinational spaceflights—or, for that matter, the private space stations and interplanetary settlements that are envisioned by Elon Musk, Jeff Bezos and other tech multibillionaires?NASA and its partners have started drafting frameworks, like the Artemis Accords—agreements signed by more than 50 nations to govern behavior in space. But even those don’t address many intimate details of death.What happens, for instance, if foul play is suspected?The Outer Space Treaty, a legal document drafted in 1967 under the United Nations that is humanity’s foundational set of rules for orbit and beyond, doesn’t say.Of course, not everything can be planned for in advance. And NASA has done an extraordinary job of keeping astronauts in orbit alive. But as more people venture into space, and as the frontier stretches to longer voyages and farther destinations, it becomes a statistical certainty that sooner or later someone won’t come home.When that happens, it won’t just be a tragedy. It will be a test. A test of our systems, our ethics and our ability to adapt to a new dimension of mortality. To some, NASA’s preparations for astronautical death may seem merely morbid, even silly—but that couldn’t be further from the truth.Space won’t care of course, whenever it claims more lives. But we will. And rising to that grim occasion with reverence, rigor and grace will define not just policy out in the great beyond—but what it means to be human there, too.

A Deadly Disease Is Eating Away at Caribbean Corals and Wreaking Havoc on Reefs. Could Probiotics Be the Solution? New research suggests the probiotic McH1-7 could help stop the spread of stony coral tissue loss disease among wild corals near Fort Lauderdale, Florida Scientists determined the most effective method of halting the disease was covering a coral colony with a weighted plastic bag, then injecting a seawater solution that contains the probiotic. They left the colony covered for two hours to allow the probiotic bacteria to colonize the coral. Hunter Noren Probiotics can be good for human health. Now, new research suggests they might also help protect coral reefs. A bacterial probiotic helped slow the advance of stony coral tissue loss disease—a fast-spreading and deadly condition—among wild corals in Florida, researchers report today in a new study published in the journal Frontiers in Marine Science. The probiotic may be a good alternative to antibiotics like amoxicillin, which temporarily curb the spread of the disease but must be reapplied frequently. In addition, scientists fear stony coral tissue loss disease may one day become resistant to these antibiotic treatments—just as “superbugs” that infect humans are building resistance to our own drugs. Antibiotics are meant to kill microorganisms, but probiotics are beneficial living microbes. The idea is that a probiotic can be incorporated into corals’ natural microbiomes, ideally offering them longer-lasting protection. First discovered in Florida in 2014, stony coral tissue loss disease attacks the soft tissue of more than 30 different species of coral. Without treatment, the disease eventually kills the corals, and their soft tissue falls off, revealing the white calcium carbonate skeleton below. In just weeks or months, it can devastate a whole colony. Stony coral tissue loss disease can be spread by fish that eat coral, as well as by boaters and divers who do not disinfect their gear. The condition has since expanded its range beyond Florida to reefs throughout the Caribbean. Several years ago, researchers looking at the great star coral (Montastraea cavernosa) discovered a probiotic called Pseudoalteromonas sp. strain McH1-7. Laboratory tests showed McH1-7 stopped or slowed the progression of stony coral tissue loss disease in infected corals. It also helped prevent the disease from spreading to healthy corals. But that was in the lab. Would McH1-7 be similarly effective in the ocean? Researchers were eager to find out, so they set up an experiment on a shallow reef off the coast of Fort Lauderdale. Study co-author Kelly Pitts, a research technician with the Smithsonian Marine Station, applies a paste containing the probiotic directly onto the disease lesion of an infected coral. Hunter Noren Experimenting with wild corals For the study, the scientists focused on 40 great star coral colonies that were showing symptoms of stony coral tissue loss disease. In one experimental condition, the researchers made a paste that contained McH1-7 and applied it directly onto the disease lesions. For comparison, they also applied the same paste, minus the probiotic, to some corals. In another condition, they covered infected coral colonies with weighted plastic bags, then filled the bags with seawater solutions made with and without McH1-7. They left the corals covered for two hours. “This created a little mini-aquarium that kept the probiotics around each coral colony,” says study co-author Valerie Paul, head scientist at the Smithsonian Marine Station at Fort Pierce, Florida, in a statement. The scientists completed all the treatments within the first 4.5 months of the project. Then, they returned periodically to gather tissue and mucus samples from the corals to measure changes to their microbiomes. Over the next 2.5 years, they took photos from a variety of different angles, which they then used to create 3D models that could track the disease’s progression. In the end, the results suggest covering the corals with plastic bags filled with the probiotic seawater solution was the most effective method. More than two years post-treatment, the colonies that received the probiotic bag had lost just 7 percent of their tissue, while colonies in the control bag condition faced 35 percent tissue loss. Scientists applied a probiotic paste directly to disease lesions on some corals. Kelly Pitts The probiotic paste, by contrast, appears to have made the situation worse: The corals that had the probiotic paste applied directly to their lesions lost more tissue than those treated with the control paste, which did not contain McH1-7. “We do not really know what is going on with the probiotic paste treatment,” Paul tells Smithsonian magazine in an email. But she has a few theories. It’s possible the high concentrations of McH1-7 contributed to localized hypoxia, or low-oxygen conditions that further harmed the already stressed corals, she says. Or, the probiotic could have changed the microbiome at the lesion site in some negative way. Another possibility is that McH1-7 produces antibiotics or other substances that were harmful at high concentrations. Amanda Alker, a marine microbiologist at the University of Rhode Island who was not involved with the study, wonders if this finding suggests McH1-7 is beneficial at specific dosages—a question future laboratory research might be able to answer, she tells Smithsonian magazine in an email. She’s also curious to know which specific molecular components of the probiotic are responsible for the increased tissue loss when applied as a paste. More broadly, Alker would like to see additional experiments validating the bag treatment method, but she says this “inventive” technique seems promising. “Their approach is a safer solution than antibiotic treatment methods that have been deployed to combat [stony coral tissue loss disease] in the field so far,” she says. “Further, this is a practical solution that could be implemented widely because it doesn’t require highly specialized equipment and has the ability to be used with any type of microbial solution.” Looking ahead to save reefs Probiotics are likely not a silver bullet for protecting corals. For one, researchers still don’t know exactly what causes stony coral tissue loss disease, which makes it difficult to determine how or why the probiotic works, Paul says. In addition, since the disease has spread to many different parts of the Caribbean, it might be challenging to use the bag treatment technique on all affected colonies. “We would need to develop better methods of deploying the probiotic through time release formulations or other ways to scale up treatments,” Paul says. “Right now, having divers swim around underwater with weighted bags is not a very scalable method.” The researchers have also conducted similar experiments on infected corals located farther south, in the Florida Keys. However, these tests have produced mixed results, probably because of regional differences in stony coral tissue loss disease. This is another hurdle scientists will likely need to overcome if they hope to expand the use of probiotics. “We probably need to develop different probiotics for different coral species and different regions of the Caribbean,” Paul says. Researchers returned to gather samples of tissues and mucus to see how the corals' microbiomes had changed. Hunter Noren Even so, scientists are heartened by the results of the experiments conducted near Fort Lauderdale. With more research, the findings suggest probiotics could be a promising tool for combatting the disease elsewhere. “Coral probiotics is a challenging field, because there are hundreds of different types of bacteria that associate with corals, and there are limitless experiments that need to be performed,” Amy Apprill, a marine chemist at Woods Hole Oceanographic Institution who was not involved with the research, tells Smithsonian magazine in an email. “These researchers made a major advance with their study by demonstrating the utility of whole colony treatment as well as the specific probiotic tested.” Apprill adds that, while antibiotics have been widely used to control stony coral tissue loss disease, scientists haven’t conducted much research to see how these treatments are affecting the plants and creatures that live nearby. “Using a naturally occurring bacterium for disease treatment may result in lessened impacts to other members of the coral reef ecosystem,” she says. Amid rising ocean temperatures, scientists expect to find even more diseased coral colonies in the future. Warmer waters may also allow other pathogens to thrive and proliferate. Against that backdrop, Apprill adds, probiotics and the different methods of applying them will be “major allies” in the fight to save coral reefs. Paul is also optimistic. Through research and field studies, she’s confident researchers will be able to develop interventions that can “help corals better survive changing environments and respond better to diseases and bleaching,” she says. Get the latest stories in your inbox every weekday.

We may earn a commission from links on this page.In 2023, I decided to update my Apple Watch after consistently failing to wear my Series 4 for a number of years. I sold that one on Poshmark and began looking at newer models to find one with enough features to convince me to actually wear it. I opted to get a Series 8, although the Series 9 had just been released, as I was buying two: one for my mom and one for myself. As it turns out, that was a great decision.If you're searching for a new wearable or considering upgrading yours, you might also be wondering which of the older Apple Watch models is still useful today. My Series 8 is holding up beautifully three years after it was introduced, so I'm a big proponent of using older devices as long as possible. But not all Apple Watches will work as well as the Series 8 does in 2025. Don’t buy a watch Apple doesn’t support anymoreWe have to draw the line somewhere: Seven of Apple's watches are no longer supported, meaning they won't receive any software or security updates anymore. In addition, you run the risk that the watch will no longer be compatible with your iPhone or certain apps. In short, you shouldn't buy a watch that Apple doesn't support. That includes the following:Apple Watch Series 0Apple Watch Series 1Apple Watch Series 2Apple Watch Series 3Apple Watch Series 4Apple Watch Series 5Apple Watch SE (first-gen) While the company does currently support the Series 6, it is next in line to join this list. It's not clear when that will happen, but you can be sure it will. We'll see next week—when Apple reveals watchOS 26—whether the watch will be supported another year. If not, it'll be stuck on watchOS 11 for good.Performance and other generational Watch improvementsThere are considerations for older Apple Watch models that extend beyond their ability to simply run the latest operating system. With each generation, improvements are made in some form or another. For instance, the Series 4 introduced the ECG sensor, while the Series 6 introduced the blood oxygen sensor (though Apple had to disable the feature for the Series 9 and Ultra 2 in the U.S. due to a lawsuit). The Series 7 charges faster than its predecessors, and Apple has included fast charging on most watch models since (sorry, Apple Watch SE users).In general, each Apple Watch is faster than the last. Apple tends to put its newest S-Chip—the Apple Watch's processor—in its latest watch series. Simply put, a newer S-chip gives you a faster, more productive product. The Series 6 has an S6 chip, Series 7 has S7, and so on until you hit the Ultras. (The first-generation Ultra has an S8 chip like the Series 8, while the Ultra 2 has an S9 chip like the Series 9.)While there are some core features all currently supported watches share—like workout and swim tracking, sleep tracking, Apple Pay, ECG scanning, and the ability to read and respond to messages—newer models also each have some of their own special advancements and upgrades. Here's a brief list:The Series 7 introduced faster charging, a larger display, and more durable screen.The Series 8 brought temperature sensing, crash detection, and a low-power mode for conserving battery (as did the second-gen Apple Watch SE).The Series 9 debuted new gesture controls, on-device Siri access, more precise location tracking in Find My, and a display with double the brightness of the Series 8.The first-gen Apple Watch Ultra introduced a more durable titanium casing, custom shortcuts to apps and modes via the Action button, a depth gauge and water temperature sensor, more accurate GPS, a 36-hour battery life, and an emergency siren.The Apple Watch Ultra 2 introduced a display with a maximum brightness of 3,000 nits and on-device media playback. The Series 10 introduced the largest display available on a standard Apple Watch and faster charging. If you see a feature you absolutely need in a particular watch model, you'll have to spring for it. But if you just want something for core Apple Watch tasks, you can start to consider older options. Apple's watch comparison site can be a helpful tool for identifying different features among models. Battery degradation All tech degrades to some extent and the Apple Watch is no different—particularly when it comes to the battery. While there are ways to mitigate the problem, over time, the lithium-ion battery powering your wrist computer won't last as long as it used to. That might be a bigger issue than your watch's ability to download and support a new operating system. Apple's warranty doesn't cover batteries that wear down from normal use, and charges $99 for the repair, which you could instead put towards the purchase of a new watch. There is one exception: Battery service is free if you have AppleCare+ and your watch's battery holds less than 80% of its original capacity. You need to take your watch in to an Apple Store or service provider to have it tested. My watch was pre-owned, and while I have no way of knowing if it has its original battery, my battery life has not declined substantially in the two years I've been using it daily. I primarily use mine to track my workouts, vitals, and sleep, which means it's always running. I charge it while I'm in the shower and occasionally for a few minutes before bed, and that's about it. On an average day of constant notifications, mine lasts me a bit longer than the advertised 18-hour mark. Because I have little interest in the small improvements offered by the Series 9 and Series 10—like extra brightness, larger screen size, performance bumps, and advanced cycle tracking—the battery life is what would (or will) compel me to upgrade in the future, but for now, I have not noticed any problems. I asked my mom if she's noticed any battery degradation on hers, since I bought it at the same time and place as mine, and she said no. She uses hers to track walking workouts, talk on the phone, and monitor her sleep and vitals, too.Stick with the Series 7 or newerThoroughly consider which of the features on newer models are actually important to you before making any buying decision and, if you can, stay above a Series 7. The Series 6 is still functional, but, again, it's a matter of time until the company stops acknowledging that one completely. For now, I have been pleasantly surprised by how well my Series 8 has held up for two years. Its touchscreen has never faltered, the external buttons function perfectly, it syncs to all of my apps and devices with no problem, and it does exactly what I need it to do—which is to tell me how many steps I'm taking and how hard I'm exerting myself at the gym. If you're in the market for a smart watch, I see no reason that an older version shouldn't be considered, as long as it still runs the latest operating system. You can save a chunk of change by sourcing an older model from the resale or refurbished markets and put that money away for when Apple drops something super revolutionary in the wearable space. Apple doesn't sell anything below a Series 10 or SE directly anymore, so if you want a 6, 7, 8, or 9, you'll have to check the resale and refurbished markets. You'll definitely save some money that way (a new Series 10 starts at $399, though it can be found on sale, and the refurbished Series 8 I got is selling right now for $219). Apple Watch Series 8 (Renewed) $209.00 at Amazon $220.00 Save $11.00 Learn More Learn More $209.00 at Amazon $220.00 Save $11.00

June 2, 20253 min readThe World Isn’t Ready for the Mental Health Toll of Extreme HeatTemperatures are rising, and so are mental health risksBy Madhusree Mukerjee edited by Dean VisserA man walks with an umbrella to protect himself from the heat as a yellow alert is issued by the UK Health Security Agency (UKHSA) due to increasing temperatures in London, United Kingdom on June 25, 2024. Rasid Necati Aslim/Anadolu via Getty ImagesThe coming summer is forecast to be a scorcher across the U.S. And climate scientists predict that at least one of the next five years will beat 2024 as the hottest year ever recorded globally. As heat waves are getting more intense and prolonged, their effect on the mind and body are also becoming more dire. Children and older people, as well as those who work outdoors, are most at risk. So are those with mental health disorders.Heat waves are the single highest cause of weather-related deaths in the U.S., where an estimated 1,300 fatalities from heat stroke and other temperature-related complications occur every year. Even those who survive a period of extreme heat may suffer serious neurological or other mental-health-related disorders.A new study published in Current Environmental Health Reports finds that the world is startlingly unprepared to deal with the mental health consequences of climate change. Of 83 action plans for heat-related health problems that were reviewed for the study, fewer than a third acknowledged the mental health effects of extreme or prolonged high temperatures. And only a fifth of these plans outlined specific actions to deal with contingencies such as increased hospitalizations for mental health disorders.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.How does extreme heat affect the brain?The human body operates optimally at 98.6 degrees Fahrenheit (37 degrees Celsius). If a person doesn’t drink enough water when the weather is hot and dry, the body becomes dehydrated, the blood thickens, and the heart may not be able to pump enough oxygen to the brain. Additionally, the human brain burns up 20 percent of the body’s energy and therefore needs to dissipate heat efficiently. In hot and humid conditions, sweating cannot cool the body and brain enough. This can lead to heat exhaustion, which has symptoms such as weakness, dizziness and headaches and, in extreme cases, heat stroke—which can then trigger delirium and loss of consciousness. A significant fraction of heat stroke survivors suffer neurological complications.Exposure to extreme heat can also increase the risk of suicide and can worsen schizophrenia, epilepsy, anxiety, depression, substance use disorder, neurodegenerative disorders (such as Alzheimer’s disease) and negative emotions such as fear and anger. It may worsen sleep, which, in turn, can increase fatigue and impair cognition. Alcohol and recreational drugs, as well as certain medications used to treat mental illness, such as antidepressants, tranquilizers and antipsychotics, also appear to increase mental health vulnerability to heat.Studies find an increased risk of suicide and epileptic seizures during heat waves, as well as an increase in hospitalizations and emergency-room visits for mental health disorders. Heat can also disorient thinking, making people slow to realize that they need to seek shelter or help.Who is most at risk?The most vulnerable are those with existing mental health disorders. Disturbingly, prolonged heat waves also appear to worsen the risk among young children—and even the unborn—of developing mental health ailments in the future. Older people may also be particularly affected, such as by accelerated dementia and Alzheimer’s.At particular risk are vast populations around the world who live without air-conditioning, including poor or homeless people and those who work outdoors, such as on farms.What can be done?The authors of the new Current Environmental Health Reports study point to interventions at several levels to help communities and individuals most at risk of climate mental health impacts. These can include public awareness campaigns, such as warning people about the mental health risk of consuming alcohol or other drugs during heat waves. Other interventions include establishing community cooling shelters for heat emergencies and increasing monitoring of mental health patients during heat waves. Extreme heat is here to stay, at least for the foreseeable future. We need to prepare people and communities to reduce the risk of mental health emergencies.IF YOU NEED HELPIf you or someone you know is struggling or having thoughts of suicide, help is available. Call or text the 988 Suicide & Crisis Lifeline at 988 or use the online Lifeline Chat.