These cases do not involve immunologic reactions, but may stem from an interference with an enzyme called prostaglandin synthetase. Another mechanism is involved in hereditary angioedema , a potentially fatal inherited disease that produces episodic swelling of the face and extremities. In addition, swelling may occur in the tongue, throat, or larynx, shutting off air to the lungs. This disease is associated with a deficiency of a blood protein that is part of the complement system. An associated disorder is dermographism , a hive that appears when the skin is briskly stroked with a firm object and which may be an allergic reaction involving IgE but without a defined antigen.
Solar urticaria follows exposure to the sun or a sun lamp.
Recurrent episodes of hives, if there is no underlying illness, are best treated with antihistamines. The effectiveness of this treatment varies, and often different types of antihistamines must be tried before one is found that relieves itching and swelling, and prevents further outbreaks. When the type of disorder can be identified, specific drugs give the best results. For example, acquired cold-induced urticaria frequently may be controlled with the antihistamine cyproheptadine, and cholinergic urticaria may be improved with the antihistamine hydroxyzine. Life-threatening hereditary angioedema can now be treated effectively with hormones.