Can a person's eyes get steamed up?

I’ve noticed sometimes when I am drinking a cup of hot coffee or cocoa, that if I lightly exhale onto the surface of the drink and the steam rises towards my eyes, my vision becomes “frosted” as if I am looking through a pair of steamed-up glasses. When I blink, the effect is immediately gone. Anybody got the straight dope on this weird phenomenon? Is it my eyelashes getting water droplets on them that causes the illusion, or can a person’s eyes actually steam up?



Your eyes must be wet, being mucous membranes and all so they can’t get “steamed up” in the normal sense.

Hot steam can certainly irriate your eyes, but getting “steamed up” implies a condensate has formed on the surface of the eyeball, and unless you’re wearing contacts it’s difficult to see how this can happen as the eye surface is (I think) too warm for this to happen.

Do you perhaps have glass eyes?

It’s simple, really. Anytime you have a cup of coffee in room-temperature air, vapors rise above the cup and re-condense into mist when they contact the cooler air. A lot of it goes right back into the cup, but not all of it. That’s why your hand will smell of coffee after you’ve had a cup, and that’s how you get a little coffee mist in your eyes.

A safety note! The same process can poison you if you drink coffee in a place with hazardous fumes. If you take hot coffee into a room with solvent fumes, that same evaporation-condensation cycle will condense solvent along with the coffee. After a few minutes, your coffee with have a little solvent in it. Ick.

Well until someone more knowledgeable comes along, I’ll point out that this happens to me, and I always assumed it was steam collecting on my eyelashes (blinking would effectively clear that).

:confused: “Steam” doesn’t collect as steam but condensation droplets. If condensation was collecting on your eyelashes, your vision would not be blurred as your eyelashes are not in your line of sight. What am I missing here?

I’ve noticed this too, but I always thought it was more a physical reaction due to the very warm temperature of the rising air/steam.

Say, haven’t you ever put drops in your eyes? Or come out of a pool without squeezing your eyes shut? Extra fluid on the surface of the eye certainly does interfere with clarity. I think it’s unlikely that the water vapor from the coffee would condense on a surface that’s close to 100 degrees F, but if there’s a way for it to collect there, I think it would, in fact, cloud up someone’s vision.

Your corneas are kept moist at all times (or should be). They’re also very warm. The only way I could see a noticible layer of condensation forming on them is if your corneas were dry and cool.

For a simple demonstration of the principle, splash warm water on a mirror and hold it near a steaming mug of coffee (or other piping hot liquid). You’ll notice, if the surface of the mirror has a layer of water on it, you don’t see “steam”. That’s because the “steam” you see on a relatively cool, dry mirror is actually a fine collection of tiny water droplets that refract and scatter light in such a way as to make a translucent layer. If there is already a continuous sheet of water on the mirror, the water vapor, when it cools, simply adds to the volume of this sheet, and refracts light no differently than any thin sheet of water would. In other words, its completely transparent.

Your lacrimal glands are constantly supplying the surface of your eyes with salinous liquid, and blinking spreads this liquid out over the eyeball and cornea; this keeps the eye lubricated and protect its cells and their essential optical properties, as well as supplying those cells with needed oxygen and nutrients. I think your eyes could survive brief periods of complete drying, but prolonged drying would most certainly cause damage.

So, while I think it is theoretically possible for eyes to be clouded by steam in a manner analogous to steam on a mirror or window, if your eyes are in such a state, your vision is probably already compromised. Grab some eyedrops and get thee to an emergency room, because you’ve got problems!

… if, of course, you can find your way there.