Blushing is a sudden reddening of the skin, induced by various mental states, particularly those involving shame or humiliation, shyness or modesty. It usually affects only the face and neck; rarely among civilised peoples the breast and other parts of the body. But 'the men of certain races, who habitually go nearly naked, often blush over their arms and chests, and even down to their waists' (Darwin). It is often accompanied by expressive movements; the face is turned aside, the eyes cast down or restlessly moved. It causes increased heat of the parts affected, with a sensation of heat and tingling, and often a general feeling of discomfort. It does not occur in young children.
Blushing is an excellent illustration of the control exercised over the circulation of the blood by the nervous system. Under ordinary circumstances, the muscular coat of the small arteries throughout the body is constantly maintained in a state of partial contraction by means of the nerves distributed to it (vasomotor nerves; see NERVOUS SYSTEM). The blood propelled into them by the heart is thus prevented from distending them to their full extent, and its passage to the capillaries in connection with them is controlled. When, however, from any cause the action of these nerves is suspended, the arteries under their influence at once dilate, the corresponding capillaries become fuller, and the tissues containing them appear much redder than in their ordinary condition.
Under the influence of shyness, shame, &c. an alteration takes place in the nervous influence proceeding from the brain, which, for the time, lessens or stops the action of the nerves controlling the arteries of the skin of the face and neck, and blushing is the consequence. Why it should result from these and not from other mental states, and why the effect should be confined in general to the face and neck, are much more intricate questions, which cannot be discussed here. For one answer to them, with many interesting facts on the subject, see Darwin, Expression of the Emotions, chap. xiii.