Mercurochrome allergy. Immediate and delayed hypersensitivity

We describe eight patients suffering from Mercurochrome allergy. Patch and prick tests were carried out with the following organic and inorganic mercury compounds: thimerosal, Mercurochrome, phenylmercuric acetate, phenylmercuric nitrate, metallic mercury, and mercuric chloride, and with sodium fluorescein. Two patients had an anaphylactic reaction a few minutes after application of Mercurochrome. The prick tests with Mercurochrome were positive and they were negative with the other tested products. All patch tests were negative. In the other six patients, the clinical picture was local eczema, and the patch tests were all positive with Mercurochrome and the inorganic mercuric derivatives. Positive patch tests with thimerosal were found only in two patients, and only one had a positive patch test with salts of phenylmercury. In four patients, the prick test with Mercurochrome, negative in immediate reading, gave a late eczematous reaction.