Blushing occurs when the blood vessels of the head and neck dilate and become infused with blood. It is an instantaneous physical change seen on the surface but reflecting a feeling of embarrassment or happiness that is held inside. When it happens I can’t control it. That point is important. My blushes betray a feeling and, even when they increase my embarrassment, I cannot stop them.
Suzanne O'Sullivan @ 5x15 — The reality of imaginary illness on YouTube.com.
One article on PainScience.com cites this item as a source: