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I noticed people who wear glasses clean the lenses by first breathing on them and then wiping it with something like a tissue or cloth etc.

Does this actually help?

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    $\begingroup$ Probably worth using a specially designed cloth, else your may scratch your glasses. $\endgroup$
    – Virgo
    Commented Aug 5, 2017 at 23:48

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It depends. Your exhaled breath is about 37 degree C and 100% relative humidity. If the temperature of the lenses are less than 37 degrees then water from your breath will condense on the lenses. This water is nearly pure (distilled purity) and can help dissolve any dirt, film that has attached to the lens.

But if the lenses are hotter than 37 degrees, you get no condensation, so breathing on the lens doesn't help. In this case just lick the lens.

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    $\begingroup$ +1 but I ain't licking no lens, no way $\endgroup$
    – user163104
    Commented Aug 6, 2017 at 21:37
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    $\begingroup$ Licking it would be a HORRIBLE idea as our saliva is EXTREMELY impure when it comes to water purity which would smudge the glasses. Also, water, to my knowledge condenses at 100 degrees Celsius. Could you point out the source for the condensation at 37 degrees too? $\endgroup$ Commented Aug 22, 2017 at 16:10
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Yes , the air we exhale contains a very high percentage of water vapour which condenses upon contact with the glass. Thus when a tissue is used to wipe it, the dirt comes off easily as it is generally soluble in water.

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