Complete Summer Heatstroke Prevention Guide: Recognizing Symptoms, Emergency Response, and Prevention Practices
From early heatstroke symptoms to severity classification, first aid procedures, and prevention through hydration and salt intake. Covers WBGT index reading, AC settings, and heatstroke alert usage.
What Is Heatstroke? Understanding the Mechanism
Heatstroke is a health disorder caused by thermoregulatory failure in hot, humid environments, trapping heat inside the body. In Japan, patient numbers surge from June to September annually; in 2023, about 90,000 people were emergency-transported nationwide (Fire and Disaster Management Agency data).
How Heatstroke Occurs
- Body Temperature Rise: High temperature and humidity prevent sweat evaporation, failing to lower body temperature
- Dehydration: Heavy sweating loses water and salt (sodium) from the body
- Reduced Blood Flow: Dehydration thickens blood, decreasing blood flow to brain and organs
- Thermoregulatory Failure: Sweating stops, body temperature exceeds 40°C (heat stroke)
High humidity days are especially dangerous. Even at 30°C, humidity above 70% hinders sweat evaporation, sharply increasing heatstroke risk.
Heatstroke Symptoms and Severity Classification (Grades I, II, III)
Based on Japanese Association for Acute Medicine classification, heatstroke is divided into three stages.
Grade I (Mild): Manageable with On-Site First Aid
- Symptoms: Dizziness, lightheadedness, muscle cramps, heavy sweating
- Response: Move to cool place, hydrate with water and salt, loosen clothing
- Recovery target: Symptoms improve within 30 minutes
Grade II (Moderate): Medical Transport Required
- Symptoms: Headache, nausea, vomiting, fatigue, weakness, impaired concentration/judgment
- Response: Call 119 immediately, cool body in a cool place
- Key judgment: If "unable to self-hydrate," call ambulance immediately
Grade III (Severe): Life-Threatening, Emergency Transport Essential
- Symptoms: Altered consciousness (no response to calls), convulsions, hyperthermia (40°C+), inability to walk straight
- Response: Call 119, cool neck/armpits/groin, check breathing
- Danger signs: "Sweating has stopped," "Skin is dry"
Important: For Grades II and III, don't hesitate to call an ambulance. Heatstroke progresses rapidly and can become severe within hours.
Heatstroke Risk CheckerEstimate Wet Bulb Globe Temperature (WBGT) and heatstroke risk from temperature and humidity.Heatstroke First Aid: 5 Steps
Step 1: Move to Cool Place
- Air-conditioned room, shade, well-ventilated area
- Cars are dangerous (interior can exceed 50°C even with windows open)
Step 2: Loosen Clothing and Cool Body
- Cool neck, armpits, groin with wet towels/ice packs (where large blood vessels pass)
- Spray water with mist, fan (evaporative cooling lowers temperature)
Step 3: Hydrate with Water and Salt
- Oral rehydration solution (OS-1, etc.) is optimal (ideal water-sodium balance)
- Sports drinks acceptable (high sugar content, so dilute 2x with water)
- If unable to self-drink, call ambulance
Step 4: Monitor Recovery Status
- If symptoms don't improve within 30 minutes, seek medical care
- If consciousness is confused or vomiting continues, go to hospital immediately
Step 5: Rest After Recovery
- Even after symptoms subside, avoid strenuous exercise for 2-3 days
- High recurrence risk, don't overdo it
7 Heatstroke Prevention Strategies
1. Check WBGT Index (Heat Index)
WBGT (Wet Bulb Globe Temperature) is a heatstroke risk indicator combining temperature, humidity, and radiant heat. Updated daily on Japan's Ministry of the Environment "Heatstroke Prevention Information Site."
| WBGT | Risk | Action |
|---|---|---|
| 31°C+ | Dangerous | Cancel exercise in principle |
| 28-31°C | Severe Alert | Cancel intense exercise |
| 25-28°C | Alert | Take active breaks |
| <25°C | Caution | Frequent hydration |
2. Frequent Water and Salt Intake
- Target 1.5-2 liters/day
- Ideal 0.1-0.2% salt concentration (1-2g salt per liter)
- Drink before feeling thirsty (thirst indicates mild dehydration)
3. Use AC Appropriately
- Target room temperature ≤28°C, humidity 50-60%
- Discard misconception "AC is bad for you" (heatstroke is more dangerous)
- Combine with fan to save electricity while staying comfortable
4. Breathable, Moisture-Wicking Clothing
- Cotton, linen, polyester mesh are ideal
- Avoid black clothes (absorb heat easily)
- Use hats/parasols to block direct sunlight
5. Don't Overexert When Sleep-Deprived or Unwell
- Sleep deprivation, hangover, or illness doubles+ heatstroke risk
- Previous night's alcohol consumption causes dehydration via diuretic effect
6. Extra Caution for Elderly and Children
- Elderly: Less sensitive to heat, less aware of thirst
- Children: Immature thermoregulation, higher perceived temperature from ground reflection
7. Use Heatstroke Alert System
- Jointly issued by Ministry of Environment and Japan Meteorological Agency (5 PM prior day, 5 AM same day)
- Alert days recommend canceling exercise and refraining from outings
High-Risk Groups and Situations
High-Risk Groups
- Elderly (65+): Declined thermoregulation
- Infants/Toddlers (0-4): Undeveloped thermoregulation
- Obese individuals: Heat trapped in body
- Chronic conditions: Diabetes, heart disease, hypertension, etc.
Dangerous Situations
- Outdoor sports: Especially right after rainy season ends with sudden heat
- Inside vehicles: Interior exceeds 50°C in just 15 minutes
- Indoor work: Poorly ventilated factories, warehouses, kitchens
- Nighttime: Heatstroke occurs even on tropical nights (minimum 25°C+)
Oral Rehydration Solution vs Sports Drink
| Item | ORS (OS-1) | Sports Drink (Pocari, etc.) |
|---|---|---|
| Sodium concentration | High (50mEq/L) | Low (20mEq/L) |
| Sugar content | Low | High |
| Absorption speed | Fast | Normal |
| Use case | Dehydration/heatstroke | Daily hydration |
Conclusion: ORS is optimal for mild-moderate dehydration/heatstroke. Sports drinks are fine for daily hydration but cause sugar excess if overconsumed, so combine with water.
FAQ: Heatstroke Questions
Q1. I dislike AC and don't use it. Is a fan alone sufficient?
A. On days exceeding 35°C, fans alone cannot prevent heatstroke. Fans only "blow air" without lowering room temperature, effectively exposing you to hot air continuously. Set AC to 28°C with "low" fan speed to minimize physical burden while preventing heatstroke. If concerned about electricity costs, check your municipality's "AC purchase subsidies" or "electricity cost assistance programs."
Q2. Is water alone insufficient for hydration? What about tea or coffee?
A. Sweating loses both water and sodium (salt). Drinking only large amounts of water can dilute blood sodium concentration, causing "hyponatremia." Additionally, coffee and green tea have diuretic effects, potentially causing dehydration. Ideal is ORS or sports drink + salt-containing meals.
Q3. Are people who've had heatstroke more prone to it again?
A. Yes, those who've had heatstroke have higher recurrence risk. The reason is temporarily declined thermoregulatory function, reducing heat tolerance. Even after recovery, avoid strenuous exercise for 2-3 days and continue conscious hydration. Heat acclimatization may also be delayed in subsequent years, so act cautiously.
Summary: "Prevention" Is the Greatest Heatstroke Countermeasure
Heatstroke is life-threatening but preventable with proper precautions and early response. Follow this checklist:
- ☑ Check WBGT index (heat index) daily
- ☑ Hydrate 1.5-2 liters/day (don't forget salt)
- ☑ Set AC ≤28°C, humidity 50-60%
- ☑ Wear hat/parasol and breathable clothing outdoors
- ☑ Don't overexert when sleep-deprived or unwell
- ☑ Extra caution for elderly and children
- ☑ Move to cool place at symptom onset; call ambulance for Grade II+
Don't assume "I'll be fine." Having accurate knowledge and vigilance about heat protects you and your family's lives.
