Heatstroke

Untreated, this medical emergency can result in permanent disability or death. Someone suffering from heatstroke—defined as a core temperature of 104°F but sometimes as high as 106°F—may appear confused and require immediate cooling, ideally with an ice bath.

When core body temperature soars to 104°F or higher and remains there for about 30 minutes, it sets off a cascade of problems in the body. Proteins and cell membranes can degrade and begin to leak, potentially leading to liver damage, blood clots, GI tract damage, and organ failure, among other issues.

Often characterized by collapsing while exercising in the heat with intense sweating, this type of heatstroke among otherwise healthy people occurs when the body loses the ability to cool itself during intense exercise and the body's core temperature has risen to 104°F or higher and cannot cool itself. If treated quickly, it's often survivable, though it can cause lasting damage.

One often-cited average estimate of annual American heat deaths — roughly 1,200 per year—is based on death certificate data, but it may be a significant undercount because heat kills through cardiovascular, kidney, and respiratory causes that are more likely to be cited on those documents. (Separate analysis that looked at data from 1999 to 2023 found that the highest number, in 2023, was 2325.)

Between 2000 and 2009 one study suggests annual heat deaths averaged around 2,670, but between 2010 and 2020 that figure was likely more than 4,000. Researchers studied 54 million death records from the contiguous US and created mathematical models to arrive at these figures, noting that a combination of aging populations and climate change drove that increase.

Floods are a distant second, followed by hurricanes. That's according to data reported by the National Oceanic and Atmospheric Administration.

Some research suggests that our gut microbiome influences our risk of exertional heatstroke. If exercise boosts our body temperatures to unsafe levels, increasing gut permeability, that can cause a "leaky" gut—allowing bacteria and other gut microbes to leak into the bloodstream and potentially trigger endotoxemia, a potentially life-threatening inflammatory response that can occur with heat exhaustion and heatstroke.

Severe illness from extreme heat exposure can alter DNA through epigenetics—turning genes "on" or "off" to shape disease risk. These changes can place an organism at greater risk of future health complications—unlike the epigenetic changes produced by moderate, repeated heat exposures.

Eric Klinenberg wrote a book diving into the specifics of the heat wave. His book, detailing the stories and context fueling more than 700 deaths during just one summer week, helps readers understand how social infrastructure lapses, power outages, and ineffective heat responses led to so many deaths.

America is generally experiencing more frequent extreme heat days, over a longer period, in certain parts of the country. The heat-related death toll is rising, and beyond those direct deaths, extreme heat can also have troubling ripple effects including elevated violence and decreased productivity.