2 doctors weighed in:
Why is your breath cold when you blow out with small mouth and warm with a wide-open mouth?
2 doctors weighed in

Dr. Richard Bensinger
Ophthalmology
1 doctor agrees
In brief: Velocity of air
When you mouth is open wide, the velocity of the air exhaled, which is humid, is not enough to cause evaporation and so your mouth stays warm. When you purse your lips, the air velocity is high and the water on your mouth and lips evaporates which cools down the tissue.

In brief: Velocity of air
When you mouth is open wide, the velocity of the air exhaled, which is humid, is not enough to cause evaporation and so your mouth stays warm. When you purse your lips, the air velocity is high and the water on your mouth and lips evaporates which cools down the tissue.
Dr. Richard Bensinger
Dr. Richard Bensinger
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