And as a practical matter, it doesn't really clarify the pronunciation of Nguyen unless one knows which English pronunciation of ng you're referring to. I'm just teasing with this pedantry, of course; I understood what you meant. But then, I already knew how to pronounce Nguyen.
What are bruises? Bruises are bluish or purple-coloured patches that appear on the skin when tiny blood vessels, called capillaries, break or burst underneath. The blood from the capillaries leaks into the soft tissue under your skin, causing the discolouration.
First, if dark circles are caused by a visible network of blood vessels under the thin eyelid skin, then making the vessels smaller might reduce the darkness. Second, constricting the blood vessels could reduce the potential for leakage of fluid from within the blood vessel, and this might reduce puffiness.