Heat Stroke

A life-threatening medical emergency where body temperature exceeds 40°C and the body can no longer cool itself. Untreated heat stroke kills within hours.

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What is Heat Stroke?

Heat stroke is a medical emergency in which the body’s internal temperature rises above 40°C (104°F) and its cooling mechanisms — primarily sweating — fail. The brain, heart, kidneys, liver and muscles begin to break down within minutes. Untreated heat stroke is fatal in 50–70% of cases; even with treatment, mortality remains around 10%.

It is the most dangerous condition in the spectrum of heat-related illness. Earlier stages — heat cramps, heat exhaustion — are warning signs. Heat stroke means the body has lost the fight.

In South Asia, heat stroke kills more people each year than cyclones, earthquakes or floods. The official tally is around 2,000–4,000 deaths per year in India and Pakistan combined, but the true toll is likely much higher because rural deaths are often unreported and cardiovascular deaths during heatwaves are not always attributed to heat.

Symptoms of heat stroke

Heat stroke can develop suddenly — within an hour — or gradually over a day. Warning signs:

Early (heat exhaustion):

Heavy sweating, cold and clammy skin
Headache, dizziness, nausea
Muscle cramps
Rapid pulse
Extreme thirst

Heat stroke (medical emergency):

Body temperature above 40°C
Skin becomes hot and dry — sweating stops
Severe headache, confusion, slurred speech
Rapid breathing, racing pulse
Loss of consciousness or seizures
Skin may be red and flushed

If you see these signs, call emergency services immediately. Heat stroke is as dangerous as a heart attack or stroke — every minute matters.

Who is at highest risk

Outdoor workers — construction labourers, farmers, street vendors, rickshaw pullers, traffic police. Most South Asian heat-stroke deaths occur in this group. India’s Labour Bureau estimates 75 million outdoor workers face severe exposure during May–June heatwaves.

Children and the elderly — children cannot regulate temperature efficiently; the elderly often have impaired thirst response and pre-existing conditions.

People with chronic illness — heart disease, diabetes, kidney disease, COPD, obesity, and certain medications (diuretics, beta-blockers, antihistamines, antidepressants) increase risk.

People without air-conditioning — heatwave deaths concentrate in homes without cooling. India’s AC penetration is only ~10%, and Pakistan’s is similar, leaving most of the population dependent on fans, evaporative coolers and shade.

Athletes and military trainees — high exertion in hot environments without acclimatisation has caused mass casualty events.

First aid for heat stroke

Before emergency services arrive, rapid cooling can save a life. Every minute the core temperature stays above 40°C, organ damage accumulates.

Call emergency services (108 in India, 1122 in Pakistan, 999 in Bangladesh).
Move the person to shade or an air-conditioned space.
Remove excess clothing.
Cool the body aggressively by any available means:
- Ice-water immersion (most effective) — a bathtub or large container.
- Wet sheets and continuous fanning.
- Ice packs on neck, armpits, groin (areas with large blood vessels close to skin).
- Cold-water spray with airflow from a fan.
If conscious, offer cool water in small sips. Do not give alcohol or caffeine.
Do not give fever-reducing drugs (paracetamol, ibuprofen) — they do not work for heat stroke and may worsen liver damage.
Monitor airway and breathing — be ready to perform CPR if needed.

The goal is to lower core temperature below 39°C within 30 minutes.

Heat stroke prevention

During heatwave alerts (IMD code orange/red, PMD code red, BMD heatwave warning):

Avoid outdoor activity between 11 AM and 4 PM.
Drink water continuously — 250 ml every 30 minutes during exertion. Don’t wait until you are thirsty.
Wear loose, light-coloured cotton clothing. Cover head and neck.
Use shade, parasols, wet towels during unavoidable outdoor time.
Eat small meals with high water content (cucumber, watermelon, coconut water, lassi). Avoid heavy oily meals.
Limit alcohol and caffeine — both increase dehydration.
Check on elderly relatives daily — many heatwave deaths occur in single-occupancy homes where no one notices the person collapse.
Never leave children or pets in parked vehicles — interior temperature can exceed 60°C within 20 minutes.

Acclimatisation: Healthy adults adapt to heat over 7–14 days of progressive exposure. New arrivals to hot climates (tourists, migrant workers, military recruits) are at much higher risk in their first week.

Heat stroke in South Asia 2025

The April–June 2025 pre-monsoon heatwave broke records across the subcontinent. Delhi recorded 49.9°C in May 2025; Pakistan’s Mohenjo-daro recorded 52.5°C. Hospitals across northern India and Punjab Pakistan reported surges in heat-stroke admissions. The death toll was estimated at over 5,000 across India and Pakistan combined — among the deadliest heatwaves of the decade.

For 2026, IMD has forecast above-normal pre-monsoon temperatures over northwest India. Cities likely to face the highest heat-stroke risk include Delhi, Lucknow, Patna, Jaipur, Ahmedabad, Hyderabad, Lahore, Multan, Jacobabad and Karachi.

Mausam Online displays feels-like temperature, heat advisory codes, and humidity on every city page. During heat alerts, check before stepping outside.

Frequently asked questions

What is the difference between heat exhaustion and heat stroke? Heat exhaustion is the warning stage — heavy sweating, weakness, nausea, normal or slightly raised temperature. Heat stroke is the emergency — temperature above 40°C, sweating may stop, mental status changes, possible unconsciousness. Heat exhaustion can be treated at home; heat stroke requires hospital care.

At what temperature does heat stroke risk begin? Risk rises sharply when air temperature exceeds 37°C with high humidity, or 42°C in dry conditions. The combined wet-bulb temperature is the most accurate predictor — above 31°C wet-bulb, healthy adults face heat-stroke risk during prolonged outdoor exertion; 35°C wet-bulb is the survivability limit beyond which death can occur within hours regardless of fitness.

Can heat stroke happen indoors? Yes — and it is increasingly common in South Asian cities during nighttime heatwaves when indoor temperatures remain above 35°C even after sunset. Vulnerable people (elderly, isolated, no AC) die in their own homes during prolonged heat episodes.

How quickly does heat stroke kill? Severe untreated heat stroke can kill within 2–3 hours. Even with treatment, delayed cooling causes permanent organ damage. The faster the body is cooled, the better the outcome.

Where can I see live heatwave alerts for my city? Mausam Online shows current temperature, feels-like, humidity and heat-advisory codes on every city page. See Delhi, Lucknow, Patna, Ahmedabad, Lahore, Karachi, Dhaka.