The body has mechanisms to alter or maintain blood pressure and blood flow. There are sensors that sense blood pressure in the walls of the arteries... My WebMD Sign In, Sign Up
Perhaps while we're not watching, the denizens of Dark Shadows carry-on, caught in another inter-dimensional wing of Collinwood. If you peer out the corner of your eye, you may catch a glimmer of this shadowy activity, perhaps in Dark Shadows Collection 14, or Dark Shadows Collection 22.
(Common Causes: Seasonal Allergies, Iron Deficiency Anemia) The most well known cause of dark circles is the lack of sleep, which is actually very true. Lack of sleep tends to make the skin look paler, dehydrates the skin and lessens the circulation in the skin, which then emphasizes the shadows under the eyes.