Blushing occurs when blood vessels near the surface of the skin dilate, causing an increase in blood flow to the face. This increased blood flow makes the face appear red or flushed. Blushing is often caused by emotions such as embarrassment, shyness, or excitement, but can also be caused by physical stimuli such as exercise or hot weather. The dilation of blood vessels is controlled by the sympathetic nervous system, which is responsible for the body's "fight or flight" response.