Heat stress deaths have climbed 60% since the 1990s — How to protect against high temps this summer
Heat stress is intensifying around the world, and new research shows it can push existing health conditions into dangerous territory faster than most people expect. Here’s what you need to know.
What Is Heat Stress and Why Is It Getting Worse?
Heat stress happens when your body can’t shed heat fast enough to keep its core temperature stable. A study published June 22, 2026 in Nature Climate Change found that one billion more people now face at least one day of extreme heat stress annually compared to the 1970s.
What’s driving it isn’t only hotter days. Lead author Rebecca Emerton of the European Centre for Medium-Range Weather Forecasts found the 10 warmest nights of the year are warming roughly 0.58 degrees Fahrenheit per decade faster than the 10 warmest days. Warmer nights cut into the recovery time your body relies on between heat exposures.
Global heat-related deaths reflect that pressure, rising from about 335,000 per year in the 1990s to 546,000 annually between 2012 and 2021, a jump of more than 60% according to the 2025 Lancet Countdown report cited by the World Meteorological Organization.
Which Health Conditions Does Heat Stress Make Worse?
The World Health Organization identifies cardiovascular disease, diabetes, asthma and mental health conditions as particularly vulnerable to heat, along with a higher risk of accidents and some infectious disease transmission.
The research on specific conditions is detailed:
- Multiple sclerosis: A 2025 systematic review in the Journal of Neurological Sciences found that 67 percent of studies reviewed showed worsened MS symptoms or increased hospitalization tied to environmental heat. Heat impairs nerve signal conduction through already-damaged myelin, which is why even a modest temperature spike can cause meaningful setbacks in MS patients.
- Cardiovascular disease, respiratory disease and diabetes: A 2025 meta-analysis in Environmental Research linked heat exposure to higher morbidity and mortality across all three conditions. Each 1-degree Celsius rise in heat exposure is associated with a 2.3 percent increase in morbidity and a 1.6 percent increase in mortality among working-age adults 15 to 64.
- Anxiety, depression and cognitive function: A 2025 review in the Journal of Climate Change and Health confirmed that extreme heat worsens all three through serotonin disruption, cortisol spikes and disrupted sleep.
Heat-related mortality for adults over 65 rose roughly 85 percent between 2000-2004 and 2017-2021, the WHO reports.
Does Medication Raise Your Risk?
Yes, and it’s one of the least-talked-about heat risks. Diuretics, beta-blockers and antihistamines can all interfere with the body’s ability to regulate temperature, making it harder to cool down even when you’re doing everything else right. Pregnant women, people with obesity and people with lower cardiovascular fitness are also in the groups clinicians flag most consistently.
If you’re on any of these medications and spending time in high heat, it’s worth checking with your doctor about what extra precautions make sense for you specifically.
What Are the Warning Signs of Heat Stress?
CDC NIOSH guidance updated in March 2026 outlines three stages:
- Heat cramps: Painful muscle spasms alongside heavy sweating. This is the body’s first signal that fluid and electrolyte balance is slipping. Rest, fluids and cooling are the right response.
- Heat exhaustion: Headache, dizziness, nausea, weakness and heavy sweating with body temperature under 104 degrees Fahrenheit. This stage requires medical care, not just rest.
- Heat stroke: Body temperature at or above 104 degrees, frequent confusion and often a complete stop in sweating despite feeling extremely hot. This is a medical emergency. Call 911.
A practical self-check for any hot day: look at your urine color. Pale or clear means you’re hydrated. Dark yellow means you’re already behind on fluids, often before any symptoms appear.
How Do You Cool Down Quickly?
Move out of the heat immediately. Then:
- Get to shade or air conditioning and loosen or remove excess clothing.
- Apply cold wet cloths to the neck, armpits and groin, the highest blood-flow areas, to accelerate cooling.
- Sip cool water steadily. Avoid alcohol and caffeine, which speed up dehydration.
- Don’t rely on a fan if the heat index is in the 90s. The National Weather Service warns that moving air can push heat into the body rather than pulling it away at those temperatures. Cold water and cold compresses are more effective.
- For heat stroke, cool the person first before transporting them. Cold water immersion or iced sheets can limit organ damage in the critical minutes before emergency responders arrive.
As intentional heat practices like sauna therapy gain popularity for their longevity and recovery benefits, the distinction between controlled heat exposure and uncontrolled overheating becomes more important than ever. Knowing these signs and acting quickly is what keeps that line from being crossed.
This article was created by content specialists using various tools, including AI.
