Eli5: how come tears don’t sting our eyes even though they are salty?


Eli5: how come tears don’t sting our eyes even though they are salty?

In: 1

Tears are not particularly salty, I think what you’re used to as “salty water” would be ocean water, which is several times saltier than anything we could tolerate.

The eyes themselves are already full of “tears”, so they’re used to the salt level roughly in tears, and actually having tears run down your face, just happens when they produce more water than they already had/needed.

The salt content is rather low and is specially suited to our eyes there are three different forms of tears, basal, reflex and psychic tears. https://youtu.be/HdtC8-LApEY

My tears actually burn the living hell out of my eyes and I’ve never been able to figure out why.

Salt stings because of osmotic pressure. Water moves out of your eye cells to balance the salt concentrations inside/outside.

Tears have the same concentration of salt as the inside of your cells so that does not happen. It’s also why lubricating eye drops containing saline don’t sting either.

All of your insides are salty. All living things are basically complicated bags of slightly salty water. Your tears are no more salty than the water inside your cells, or your blood. But they do *taste* salty, so why is that? Well, your tongue is good at detecting salt, and tears *are* more salty than fresh water. Also, tears are pretty much just water and salt, unlike blood, for instance, which also has a lot of iron which gives it its distinctive flavor. You (probably) don’t think of blood as salty because that’s not its dominant flavor.

So the reason tears don’t sting your eyes is that they are exactly as salty as your eyeballs, and exactly as salty as your eyes prefer to be. Which is salty enough to taste, but nowhere near as salty as, say, sea water.