Updated

Updated · The Guardian · Sep 14

Hot Drinks Can Cool Bodies in 30C Heat as Breeze, Not Humidity, Drives Sweat Loss

Updated

Updated · The Guardian · Sep 14

Hot Drinks Can Cool Bodies in 30C Heat as Breeze, Not Humidity, Drives Sweat Loss

Q: At what exact humidity level does a hot drink switch from a clever cooling trick to a dangerous overheating risk?

There is no exact humidity percentage at which a hot drink flips from cooling to dangerous. The research cited by Prof John Tregoning and Prof Ollie Jay shows the effect depends on the full heat balance: air temperature, humidity, airflow, radiant heat, exertion, clothing, and the person’s health. Relative humidity alone is a poor cutoff because it changes with temperature. A more useful guide is whether sweat can evaporate. In dry, breezy, well-ventilated conditions, a hot drink may trigger extra sweating that evaporates and removes more heat than the drink adds. In hot, humid, still air, that evaporation is restricted, so the same drink is more likely to leave you feeling warmer. That does not mean a hot drink suddenly becomes a “dangerous overheating risk” at one threshold for everyone. Danger comes from the overall environment and the body’s inability to shed heat, not from a single humidity number. Heat scientists therefore use broader measures such as heat index, wet-bulb globe temperature, or UTCI rather than one humidity cutoff. If you want a practical rule, once conditions feel muggy and sweat is not drying—often when dew points are above about 60°F (16°C), and especially in the mid-60s to 70s°F—the cooling benefit of a hot drink is likely small or absent. In truly oppressive heat and humidity, hydration matters far more than drink temperature. Tregoning’s advice remains the safest: drink fluids in hot weather at whatever temperature you prefer.

1 articles · Updated · The Guardian · Sep 14

Prof John Tregoning said a hot drink can help cool the body in hot weather only when extra sweating is able to evaporate efficiently, such as in breezy conditions.
That effect hinges on two competing forces: the drink briefly raises body temperature, but the added sweat can remove more heat if it turns from liquid to vapor on the skin.
High humidity or poor ventilation flips the outcome because sweat runs off instead of evaporating, making a hot drink more likely to leave someone hotter rather than cooler.
Tregoning said the practical takeaway is to keep taking in fluids in hot weather—whatever their temperature—because hot and cold drinks offer no large overall advantage.

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The Guardian39d ago

Prof. Tregoning: Hot Drinks Cool in Breezy Conditions, Not Humidity

Could ice-cold drinks actually be worse for your core body temperature than a hot coffee during a dry summer breeze?

At what exact humidity level does a hot drink switch from a clever cooling trick to a dangerous overheating risk?

If climate change brings wetter heatwaves, will our natural sweating response and traditional warm fluids completely fail to cool us?

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1 total

The Guardian39d ago

Prof. Tregoning: Hot Drinks Cool in Breezy Conditions, Not Humidity

Hot Drinks Can Cool Bodies in 30C Heat as Breeze, Not Humidity, Drives Sweat Loss

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