Backgrand and Aims PACU is a specific type of urticaria which characterized by the rapid onset of pruritus, erythema, and swelling after a cold stimulus.

Studies show that the headache could be elicited only in hot weather; attempts to reproduce the pain during the winter were unsuccessful, even with use of a cold stimulus of the same temperature.

The strong stimulus can also cause the abnormal stimulation of the cold receptors.