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A 45-year-old member asked:

Why is your breath cold when you blow out with small mouth and warm with a wide-open mouth?

1 doctor answer2 doctors weighed in
Dr. Richard Bensinger
Ophthalmology 52 years experience
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.

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Last updated Dec 13, 2014

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