Extreme heat: Wet-bulb temperatures and human health

Climate Science
Written By Anonymous

Scientists traditionally focused on air temperature as a primary factor determining when humans experience heat stress. In recent years, researchers have learned that humid heat (high temperatures combined with high humidity) can threaten human health at lower temperatures than dry heat more than previously thought.

Dry heat: High temperatures paired with very low humidity, usually below 30%. Temperatures around 105°F (40.5°C) may become dangerous.

Humid heat: Wet-bulb temperature is a measurement that combines air temperature and humidity to determine how effectively the human body can cool itself through sweating. As humidity rises, sweat evaporates more slowly. A wet-bulb temperature exceeding 86°F (30°C) can put human health at risk, especially with prolonged exposure. 95°F (35°C) is considered the theoretical upper limit of human survival, even with shade, hydration, and other protective measures.

Here’s a calculator to determine your local wet-bulb temperature.

Heat exhaustion

Heat exhaustion occurs when the body is overwhelmed by heat and struggles to effectively cool itself. Symptoms may include heavy sweating, weakness, dizziness, nausea, headache, and elevated body temperature. Heat exhaustion can usually be treated by moving to a cooler area, resting, drinking fluids, and cooling the body, but it requires medical attention if symptoms worsen or don’t improve at home.

Young children, older adults, people with certain health conditions, people who are not acclimated to high temperatures, and anyone spending extended periods outdoors without enough shade or hydration are at particular risk of heat exhaustion and heat stroke.

If you or someone around you is experiencing symptoms, medical professionals recommend:

  • Moving to a shady, cool, ideally air-conditioned area

  • Cooling the body with ice packs, cold water, or ice baths

  • Wearing loose, damp clothing

  • Calling emergency services if heat stroke is suspected or symptoms are not improving with cooling and rest

Heat stroke

When the body's core temperature rises to around 104°F (40°C) or higher, it can lead to a life-threatening condition called heat stroke. Heat stroke occurs under various combinations of high temperatures, high humidity levels, activity level, hydration level, and length of heat exposure.

Symptoms include:

  • Brain dysfunction: confusion, agitation, and loss of coordination

  • Organ damage as cells begin to malfunction and break down

  • Increased strain on the heart as it works harder to circulate blood and cool the body

  • Hot, dry skin

  • Heavy sweating

  • Rapid pulse

  • Fast, shallow breathing

  • Nausea or vomiting

  • Headache

Heat stroke requires immediate medical attention.

Please note: This post provides general information about wet-bulb temperatures and heat stress. It is not medical advice. For medical advice, please consult a healthcare professional.

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