The cause of chronic hives is usually unknown. Studies suggest that between 80% and 90% of cases are idiopathic. Even with an extensive diagnosis, a cause may never be found. Dermatographism is a ...

Urticaria pigmentosa ... In cases where lesions are extensive or cause significant discomfort, phototherapy (light therapy) ...

Aquagenic urticaria is a rare condition where people have an allergic skin reaction to water. The reaction typically involves hives and bumps and can occur as often as several times a day.