Heat Stroke Isn’t Just a Short-Term Danger

With each summer of increased extreme heat, more people worldwide face the risks associated with heat exposure. Last year, Europe saw a record number of heat-related deaths, and even regions more used to dealing with hot weather, like South Asia, are seeing high temperatures start earlier and earlier in the season. Heat stroke—the most dangerous form of heat-related illness—is a growing threat and creates a public health quandary since there’s still no available treatment other than simply cooling victims down. What’s more, early research seems to suggest heat stroke could lead to further health consequences down the line. Here’s what we know about the condition now, and what experts hope research can tell us in the coming years.

The body in heat stroke

Heat stroke, which is unrelated to the cardiovascular event that shares the term “stroke,” occurs when the core body temperature rises to dangerous levels. It’s the most severe form of heat illness, a category that includes dehydration-related heat cramps, the fatiguing feeling of heat exhaustion, and even sunburn. Sometimes, a person will experience one or more of these more minor conditions prior to a heat stroke, but there isn’t always a warning.

During a heat stroke, “the body can no longer regulate temperature,” says Zachary Schlader, an associate professor of kinesiology at Indiana University, where he studies thermal stress. “It’s not just being hot.” The real danger of heat stroke, he says, is that it’s marked by some level of central nervous system dysfunction. This type of physiological malfunction causes a massive body-wide inflammatory response that quickly places just about every organ system in danger. Because of the quick and systemic threats it poses, Schlader compares heat stroke to sepsis—a whole-body infection.

Are you working outside in a heat wave? Tell us about it.

Heat stroke generally comes on in one of two ways: exposure to extreme heat, or intense activity that heats the body to those same levels. “When the environmental temperature rises, our body’s metabolism actually increases, which increases heat production,” explains Miles Marchand, a cardiology resident at the University of British Columbia. At the same time, in high temperatures “we have less ability to dissipate heat to the environment.” A healthy cardiovascular system, explains Marchand, can compensate a bit by dilating blood vessels and regulating cardiac output. This is why environmental exposure is a much greater hazard for those with cardiovascular risk factors or prior health conditions, such as the elderly.

Read More: Why Extreme Heat Is So Bad for the Human Body

When people consider the risks of heat stroke, “probably the top thing that’s underappreciated is physical activity or exercise,” says Schlader. Younger and fitter people are generally more likely to get heat stroke from prolonged physical activity in already-hot conditions. (It’s because of this that modern heat-stroke research often uses military populations as subjects).

And when it comes to treating heat stroke once it begins, rapid cooling is the only option, says Schlader. The gold standard, he explains, is basically just an ice bath. That is why heat stroke disproportionately kills those who live far from resources like hospitals and cooled public spaces, or who can’t afford the resources that would make quick cooling accessible. This is also why heat stroke is taken so seriously in the military—there is nothing helpful for a heat stroke that fits in a portable first-aid kit. As global temperatures increase, Schlader expects that more cities will begin to implement dedicated relief zones near crowded areas and build infrastructure like the cooling stations added two years ago to Saudi Arabia’s Grand Mosque for Hajj.

The lack of other treatments is part of what makes heat stroke so dangerous, says Schlader. “Rapidly cooling people requires a lot of different infrastructure that a lot of places don’t have.” Even air conditioning relies on a plentiful and predictable source of power.

Newer Research

Bringing a heat-stroke sufferer’s body temperature back to normal as quickly as possible has long been recognized as a simple matter of survival, but early research in animal models is sparking discussions about potential long-term organ damage for some survivors of heat stroke. In experiments looking at mice and rats subjected to heat stroke at extreme temperatures, researchers have identified some clear biomarkers of injury, primarily in the heart and the kidneys. Though these aren’t the only organ systems put under stress by a heat stroke, says Schlader, the roles they play in maintaining a core temperature—pumping blood and managing hydration—are critical. It makes sense that they would have long term consequences.

It’s too early to say, however, if we’re facing a future of increased heat-stroke induced trauma. It’s possible, for instance, that certain injuries to internal organs are mitigated by rapid cooling, a treatment that isn’t generally made available to animal test subjects. But fatality rates for victims climb in the years immediately following, suggesting that surviving a heat stroke leads to increased risk of cardiovascular disease, even when comorbidity is accounted for. Long-term cognitive and motor impairment has also recently been tied to heat stroke, even in young, otherwise healthy people.

Read more on extreme heat:

For those with ready access to medical care, this isn’t a concern. “In the majority of heat stroke patients that present to hospital, patients actually recover quite rapidly,” says Marchand. That’s great, if you live near a hospital. But the speed at which heat stroke worsens, and the lack of a pharmacological treatment, means that a time window that might not matter for other emergencies—like a one-hour ride to a hospital—can mean the difference between life, death, and long-term disability.

Spotting Heat Stroke

If you think there’s even a chance someone you’re with is experiencing heat stroke, it’s important to seek treatment. “Untreated, there is a high mortality rate,” says Marchand. Nearly 60% of victims suffer fatal organ failure within a few days, according to some research. Heat stroke can come on so fast and so surreptitiously that “the main warning signal should be the weather forecast,” he says.

Still, there are a few things to keep an eye out for if you’re out on a hot day. The clearest indicator of heat stroke is confusion and disorientation, caused by the “short-circuiting” of the central nervous system. At the start, this can also manifest itself as mood changes “that are kind of extreme,” says Schandler. “If someone becomes way more irritable, or starts acting very differently,” that can be a key neurological indicator of heat stroke.

“Many people will be sweaty initially, but as they become more dehydrated (particularly in older individuals) the skin may actually become dry,” Marchand adds. If you see these signs, seek help.