Here’s something I can’t get a straight answer to: what is the physiological explanation for the dark rings under one’s eyes due to fatigue, allergies, etc.? One of the answers I found stated that it’s thin skin under the eyes, and the rings are caused by blood vessels. This doesn’t add up, however, due to the fact that the colour should then be pinkish, and any increase in blood flow should enhance the rings (and not just below the eyes, as there are a number of other places on the body with thin skin). I don’t think blood flow increases just under my eyes when I’m tired, for instance.
So does anybody have a real explanation for this one?