Summary
Urticaria is a common, pruritic skin condition with multiple causes and can have a significant impact on quality of life. In this paper we present a case of acute urticaria secondary to hyperthyroidism. This link appears to be due to the autoimmune thyroid cascade (particularly IgE anti-thyroid peroxidase (TPO) antibodies) sensitising mast cells for activation and histamine release. Although anti-histamines and steroids are first-line treatment, identifying the “causative” factor is not easy in hyperthyroid patients due to the independent links urticaria shares with both carbimazole and thyrotoxicosis.