There kimkim yr ans.

Why does spit help?

Saliva contains a whole range of different substances commensurate with its multitude of functions (moisturiser, enzymatic digestion, decay fighter, lubricant, host defence, solvent for tastes etc). Its moisturising function is relatively important, just talk to someone who has had their salivary glands removed or destroyed if you're not convinced. The "skin" (mucous membrane) lining the inside of the mouth has to be relatively waterproof and this is accomplished by incorporating a number of water repelling fat like substances (lipids) in the lining cells. Unfortunately lipids will cause water to form droplets rather than a thin film on the surface. So saliva contains some surface active substances (surfactants) to break down the surface tension and promote film rather than droplet formation. Which leads us to the explanation for why spitting in the mask helps prevent misting.

Qiang

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