Understanding the Heat Index: At What Temperature Does It Become a Health Hazard?

Period of extreme heat In Thailand, many people may have heard the term “ heat index ” used in weather forecasts and health warnings, especially during unusually hot seasons, which can affect health if exposed outdoors for long periods.

Thairath Online will help explain what the heat index is and at what level it becomes dangerous to the body, helping you take proper precautions against extreme heat risks.

Getting to know the "heat index" What is it?

The heat index (Heat Index) indicates the temperature the human body actually “feels” at a given time. It depends not only on air temperature but also factors in relative humidity.

When it is hot and humid, the body's sweat evaporates less effectively, reducing heat dissipation, making us feel hotter than the actual temperature, and increasing risks of health issues such as

• heat exhaustion,
• dizziness,
• heat rash,
• and heat stroke.

Checking the 2026 heat index: At what temperature does extreme heat become hazardous to health?

For the 2026 hot weather, the heat index is divided into four levels with practical advice as follows:

1. Watch Level

• Temperature: 27.0–32.9°C
• Advice: Monitor heat warnings and maintain regular health care.
• At-risk groups: Should drink clean water frequently to prevent dehydration.

2. Warning Level

• Temperature: 33.0–41.9°C
• Advice: Reduce outdoor activities, especially between 11:00 a.m. and 3:00 p.m., when heat is most intense.
• At-risk groups: If experiencing symptoms such as dizziness, fatigue, or nausea, seek medical attention immediately.

3. Danger Level

• Temperature: 42.0–51.9°C
• Advice: Closely observe your symptoms and avoid prolonged sun exposure.
• At-risk groups: If symptoms occur, see a doctor immediately as heat stroke risk is high.

4. Extreme Danger Level

• Temperature: Above 52.0°C
• Advice: Avoid outdoor activities completely and stay in shaded or ventilated indoor areas.
• At-risk groups: If experiencing symptoms such as fainting, severe heat, or loss of consciousness, seek emergency medical care immediately.

Groups that need special care during "hot weather" include:

• Young children (0–5 years old)
• Elderly people aged 60 and above
• Pregnant women
• Patients with chronic diseases
• People with obesity
• Those who consume alcohol
• People who work outdoors for extended periods
• Outdoor exercisers and tourists

However, if the heat index is at or above the "warning level " (33.0–41.9°C), reduce outdoor activities and drink enough water. Knowing risk levels in advance helps people prevent harm from extreme heat and reduces heat stroke risk. Thank you for the information from:

Bangkok Metropolitan Administration