Three patients had allergic contact dermatitis due to exposure to orthopedic casts. In each instance, the causative agent was considered to be free formaldehyde derived from the melamine formaldehyde resin incorporated into the casts. All patients had positive patch tests to formaldehyde, and free formaldehyde was demonstrated in the cast material. Patch tests to the plaster itself were negative when fresh plaster was used but were positive with the use of aged plaster. Patch testing may afford a reliable means of differentiating true contact allergy from nonspecific irritation that may be mimicked clinically.
Logan WS, Perry HO. Cast Dermatitis Due to Formaldehyde Sensitivity. Arch Dermatol. 1972;106(5):717-721. doi:10.1001/archderm.1972.01620140061018