Why do your eyes get red when you cry?

Red eyes: This is actually a very good question and it would seem like the answer would be simple and straight forward. The most likely cause is related to a valsalva maneuver. When we cry, we often hold our breath somewhat and this retards the flow of blood into the lungs and increases back pressure on the venous side of our circulation. This causes blood vessels to be engorged, including the eye.

Frequently, yes: The tears produced by crying can be somewhat irritating to the eyes, because they are not the typical minute to minute tears that lubricate the eye (they are more like "reflex tearing", or tearing in response to something getting in the eye). Plus, with actual crying, there tends to be increased facial congestion and some degree of eye rubbing, which can worsen the redness.