We typically characterize hives as an allergic skin reaction manifested with diffuse swelling, itching, and redness. In an unusual case (with accompanying image) recently reported in the New England Journal of Medicine, a woman developed a reaction of blue hives.

The cause is not as much an enigma as it is atypical. The patient was a 77 year-old woman who underwent surgical resection of a carcinoma of her right breast. In such cases, it is standard procedure to inject a colored dye (in this case, isosulfan blue) into the lymphatic system to delineate its drainage pathway. This allows the surgeon to roughly identify which sentinel lymph nodes to excise and biopsy. The patient, unfortunately, was one of the 1.5% of patients who are allergic to the dye. She subsequently developed hives intraoperatively. Although technically the hives is not blue, the presence of dye created this visual impression.