Urticaria in a tattooed patient.

We present a case of urticaria in a tattooed patient due to hypersensitivity to the cobalt chloride contained in the blue ink used for tattoo. The patch test with the series of International Contact Dermatitis Research Group was positive only for chloride cobalt. Cobalt is believed to be responsible for contact urticaria through a non-immunological mechanism. On reviewing the literature we have found no report of contact urticaria to cobalt in tattooed patients.