Who Is Most at Risk for Heat Stroke?

Heat stroke is not random. The same hot afternoon will hit one person hard and barely register on another, and the reasons are surprisingly consistent across decades of emergency medicine and public health data. The people who end up in the ER on a heat-wave day share specific risk factors — some obvious, some less so — and understanding which ones apply to you or to someone you care about is the foundation of a real prevention plan.

This article walks through the groups most vulnerable to heat stroke, the medical conditions and medications that raise risk, the situational factors that compound it, and what each one actually changes about how the body handles heat.

A quick anchor before the list

Heat stroke happens when the body can no longer get rid of heat fast enough, core temperature rises above 104°F (40°C), and the central nervous system starts to fail. The two systems that prevent that — cardiovascular function (pumping blood to the skin) and sweating (evaporative cooling) — are what every risk factor on the list below interferes with. Some risk factors hit the sweating side, some hit the cardiovascular side, some hit both, and some change the situation so that a person stays exposed too long.

With that frame, the risk groups make more sense.

Older adults, especially over 65

Older adults are at the highest risk overall, and the reasons compound. The aging body sweats less efficiently. Thirst perception declines, so dehydration starts earlier and is recognized later. Cardiovascular reserves shrink, so the heart's ability to pump blood to the skin for cooling is reduced. Chronic conditions are more common, and so are the medications that interfere with heat regulation. Many older adults live alone, sometimes without working air conditioning, sometimes with limited mobility to relocate to a cooler space.

In nearly every U.S. heat-wave fatality study, adults over 65 — and particularly those living alone, without AC, with chronic illness — make up the majority of deaths. The fact that most of those deaths happen indoors rather than outdoors is the underappreciated piece.

If an older person in your life lives alone or relies on a single fan and an open window, a short check-in call during a heat advisory is a meaningful intervention.

Infants and young children

Children are not small adults when it comes to heat. They have a higher surface-area-to-body-mass ratio, which makes them gain heat from the environment faster. They sweat less than adults. They depend on others to recognize symptoms and to move them out of heat. And they have far less reliable ability to communicate what is happening — a toddler who is dizzy, headachy, and nauseated may just become cranky or quiet.

The most preventable cause of pediatric heat stroke death in the U.S. is being left in a parked car. A car interior can reach 120–130°F (49–54°C) within minutes on an 85°F day, even with windows cracked. There is no safe duration for any child to be left in a parked car in warm weather.

Children playing or training outdoors in heat are also at meaningfully higher risk than adults doing the same activity, and youth sports guidelines exist for exactly this reason.

People with chronic medical conditions

Several common chronic conditions raise heat stroke risk:

• Heart disease. Reduces the cardiovascular reserve needed to pump blood to the skin for cooling and to handle the strain of high core temperature.
• Lung disease. Limits the body's ability to dissipate heat through respiration and to handle the metabolic demands of overheating.
• Kidney disease. Affects fluid and electrolyte balance, both already stressed in heat.
• Diabetes. Can blunt thirst perception, impair sweating in long-standing cases, and complicate hydration management.
• Mental illness, including schizophrenia and depression. Some of the risk comes from medications (covered below), some from disrupted self-care during heat events.
• Neurological conditions. Conditions like Parkinson's disease, multiple sclerosis, and dementia can interfere with thermoregulation, recognition of symptoms, or the ability to take protective action.
• Obesity. Adds metabolic heat production, reduces heat dissipation efficiency, and increases the cardiovascular load of physical activity in heat.

None of these is a reason to avoid summer. They are reasons to plan summer more carefully — earlier hydration, more shade breaks, lower-intensity activity, indoor backup plans, conversations with a clinician about what heat means for the specific condition.

People taking certain medications

Several common medication classes meaningfully raise heat stroke risk:

• Diuretics ("water pills") reduce circulating fluid volume, making dehydration easier.
• Beta-blockers blunt the heart rate response that the body uses to deliver blood to the skin for cooling.
• Anticholinergics — including some antihistamines, antispasmodics, and overactive-bladder medications — reduce sweating.
• Certain antidepressants (especially tricyclics) and some antipsychotics interfere with central thermoregulation.
• Stimulants — including ADHD medications and some weight-loss drugs — raise baseline metabolic heat production.
• Lithium can become toxic with the fluid shifts of heavy sweating.
• Some Parkinson's medications interfere with sweating.

This list is not a reason to stop any medication. It is a reason to bring up heat planning at the next clinic visit if heat exposure is unavoidable, and to be more conservative with exertion and exposure during heat advisories.

Outdoor workers

Construction, agriculture, landscaping, roofing, road work, warehouse and delivery work without full climate control — these are the occupations with the highest rates of heat illness and heat stroke in U.S. data. The combination is direct: prolonged exertion, often in protective gear, often in the worst part of the day, often without the option to simply stop and go indoors.

Occupational safety guidance exists for exactly this group, with work-rest cycles scaled to heat index, mandatory water access, mandatory shade access, and acclimatization protocols for new workers. Where those guidelines are followed, rates drop. Where they are treated as suggestions, the ER admissions during heat waves tell the story.

Migrant agricultural workers and workers without strong workplace protections are at particularly elevated risk. Time of season matters too — most occupational heat stroke deaths happen in the first weeks on a hot job, before acclimatization has built up.

Athletes, especially during early-season training

Football players, cross-country runners, distance cyclists, marathoners, military trainees, wildland firefighters — the people in highest training loads under high heat — have an exertional heat stroke risk profile distinct from the classic risk profile.

The pattern is consistent: a young, healthy, motivated person trains hard on a hot day, often early in the season before acclimatization is complete, often pushing through early warning signs, often in a culture where stopping is discouraged. Core temperature climbs faster than sweating can cool it. Mental status changes. The person collapses.

Sports medicine has explicit acclimatization protocols, hydration plans, and heat-index-based modification guidelines. The teams and programs that follow them have far lower rates than those that do not.

Travelers from cooler climates

A person who is fully acclimatized to 75°F summers and then flies into a 100°F city is at meaningfully higher risk for the first few days. The body has not built the sweating, cardiovascular, and plasma-volume adaptations that local residents have. The mistake is to assume that "I am healthy and fit" translates to heat tolerance. It does not.

Hikers heading into desert national parks are a recurring example. So are tourists pushing through long days of walking in a hot city. The safest pattern is reduced exertion and exposure for the first three to five days, with full activity returning only after acclimatization.

People without reliable air conditioning

This is the underappreciated category. Most heat-wave deaths in U.S. cities happen in apartments without working AC, in people who could not get to a cooling center, often older adults or people with chronic illness who also could not afford to run AC even if they had it. The combination of indoor heat that does not drop overnight, dehydration, sleep loss, and medication-driven vulnerability is a recognized and preventable killer.

Community-level interventions — opening cooling centers, knocking on doors during heat advisories, distributing window AC units to high-risk households — are what move the numbers in the right direction.

People who have already had heat illness

Once a person has had heat exhaustion or heat stroke, they are at higher risk for it again. The body's thermoregulation can take weeks to months to fully recover, and in severe cases, some impairment may be permanent. People returning to activity after a heat illness should reintroduce heat exposure gradually under medical guidance.

Alcohol use

Heavy alcohol use in the 24 hours before heat exposure raises risk for several reasons — dehydration, impaired judgment, blunted thirst signaling, sometimes blunted awareness of early symptoms. This applies to the obvious cases (drinking heavily on a hot day at the beach) and to the less obvious ones (a person who had several drinks the night before a long hot hike).

Weather sensitivity and headache history

For people who are weather-sensitive — those with migraine, chronic pain, certain autonomic-nervous-system conditions, or pregnancy-related blood pressure shifts — heat tends to lower the threshold for other symptoms. The heat itself does not necessarily put a person at higher heat stroke risk per se, but the broader sensitivity to weather changes often shows up as a tendency to feel "off" earlier in a heat event. That can be useful as an early warning.

Tracking heat index alongside barometric pressure, humidity, and your own symptoms across a season makes the personal pattern clearer — the combinations of conditions that consistently produce a hard day, and the conditions that you handle without much trouble. The Pressure Pal app is built for that kind of multi-signal tracking, and the data tends to be most useful on the days when prevention decisions have a real stake.

A short summary

Heat stroke risk is highest in:

• Adults over 65, especially living alone or without AC
• Infants and young children
• People with heart, lung, kidney, or neurological disease
• People with diabetes, obesity, or mental illness
• People on diuretics, beta-blockers, anticholinergics, stimulants, certain antidepressants, lithium, or some Parkinson's meds
• Outdoor workers, particularly early in the season
• Athletes and military trainees in early-season hot conditions
• Travelers into hot climates
• People without reliable air conditioning
• People with previous heat illness
• People with heavy alcohol use in the prior 24 hours

The takeaway is not that heat is uniformly dangerous. It is that heat is uniformly more dangerous for some people than others, and knowing which category you and the people around you fall into is the start of a real plan — cooler indoor environments, earlier and gentler outdoor exposure, more conservative hydration, more shade breaks, more buddy-system awareness, and more humility on the days when conditions are stacking against you.