Among the many attempts to classify urticaria, 2 categories have been accepted worldwide, namely according to time course into acute (shorter than 6 weeks) and chronic urticaria (longer than 6 weeks) and a classification according to etiopathophysiology. A special subgroup is the physical urticarias where wheals are elicited via specific physical (mechanical, temperature, radiation) stimuli. In many forms of chronic urticaria, psychosomatic influences play a role. Despite great progress in modern immunology and allergology, chronic urticaria still remains a challenge for doctors and patients.