We release tears when our eyes are irritated, and that’s to try to wash away whatever is irritating the tissues (e.g think cutting onions, or if you accidentally poke yourself in the eye… or get a fly in there, eek).
But when we are sad (or really happy!), we cry, and that is different, even apparently, the tears themselves are different. No one really know why tears have this link to an emotional response, and other animals don’t seem to do it.
It could have evolved as a type of non-verbal communication, to show others that we are sad, so they will leave us alone or stop doing whatever it is that is hurting us. But scientists still really don’t know!!
Often you can notice the difference between irritant tears and emotional tears based on whether the eyes get red with the blood vessels being more prominent. This tends to happen in irritant tears in particular 🙂