Blushing is the reddening of a person's face due to psychological reasons. It is normally involuntary and triggered by emotional stress tying candour, such as that associated with passion, embarrassment, shyness, anger, or romantic stimulation. Severe blushing is common in people who suffer social anxiety in which the person experiences extreme and persistent anxiety in social and performance situation.
When we are anxious or embarrassed, our bodies are flooded with epinephrine, also known as adrenaline, which causes us to experience very real physiological symptoms. In addition to increasing the heart rate, suppressing the digestive system and inhibiting pain, epinephrine may also act as a vasodilator on certain blood vessels. It causes blood vessels to widen, improving the flow of blood and oxygen throughout particular regions of the body.
Blushing is an unfortunate side effect of the vasodilation of certain veins in the face. As these blood vessels in the face grow wider, the increased circulation causes the cheeks to redden. Vasodilation sometimes occurs for other reasons, including alcohol consumption and certain medical conditions.