Eli5 why is it that eyes don’t seem to get cold or even freeze.



Even when walking in -20 C weather the rest of my body will get cold and get numb, yet even though my eyes are exposed to such cold temperatures they always seem to stay warm and wet.

In: Biology

First of all tears and the film on our eyes are salty which lowers the freezing point slightly.

Secondly, your head outputs a lot of heat compared to the rest of your body. ~35% of all heat the body produces is lost through the head. This means your eyes are relatively warm compared to other parts of your body continuously heating the film. Also, your brain is the last thing to stop getting energy when your body is shutting down. Your extremities may close their blood vessels but your brain will still be getting almost all the resources it wants.

Third, your eyes blink regularly which agitates the film on your eyes breaking any crystals formed. It’s like how a river can keep flowing if there’s enough turbulence to keep breaking the ice crystals at a rate faster than they are forming.

Hahahaha laughs in Canadian. Oh yes they do. Just got out of a minus 52c cold snap and boy howdy they will freeze. Eyelashes will freeze together just from your breath, and dry them out fast.

This is a faulty premise. Eyes do get cold, but -20C is only -4F, which is not so cold that it’s hard for your blood to keep them warm. But try walking around outside at -44 (which is the same in C and F). You will feel your eyeballs get cold just like any other exposed body part.

Being cold and Feeling cold are two very different things.

Most of the time you only ‘feel’ cold. Most people have never actually been cold. The few people who have can tell you its a whole new level of indescribably unpleasant.

Your body will, as a self defense mechanism to prevent that will stop trying to heat up your extremities. (Bonus fact, this is why your girlfriends toes are freezing, women’s bodies give up on the extremities sooner than men’s) So that it preserves the heat and can keep you at a good temperature.

So your nose isn’t very important, it can get ignored while the heat keeps important bits of you running, like your heart, or brain.

So you aren’t actually as cold as you think you are. There’s a lot of heat in you, you’ve just stopped sending it to the outside bits of you so you can save it.

The other key bit here is that ‘cold’ and ‘warm’ aren’t actually about temperature, its about thermal conductivity. How easily heat transfers from one object to another. That’s why a steel pipe will feel cold but a piece of wood doesn’t. Or why a pool at 20C feels cold, but 20C is warm for air temperature.

There’s actually no such things as ‘cold’, there’s ‘heat’ or ‘less heat’. The ability of a substance to move heat around is the key here.

Air is actually *really bad* at moving heat. It qualifies as an insulator in fact. Water on the other hand is pretty good at transferring heat, that’s why you can get cold swimming no matter how hot a day it is.

Another interesting thing about water is that while its very good at transferring heat, its very good at holding onto a lot of heat too. It takes a lot of energy to heat up water, and because math always works both ways, that means you have to steal a lot of energy from it to cool it back down. And your eyeball is full of water. Making it hard to change its temperature.

Also, not much of your eye is exposed, most of it is tucked away safely inside your skull.

Simply put, your head is better at keeping your eyeball warm than the air is at taking the heat away.

-45 feels cold when you have your face covered with a balaclava but your eyes are not protected.