Propyl gallate, a ubiquitous topical product in industry, and an agent commonly found in food and cosmetics, caused contact dermatitis in five of ten people who applied it for about 20 days. Experiments in guinea pigs showed that propyl gallate has a contact sensitization potential comparable to that of dinitrochlorobenzene.
Although propyl gallate has been used as a major antioxidant in fatty materials since 1947, we have found no reports of contact sensitization in the United States. We propose that induced immunological unresponsiveness (tolerance) is responsible for this lack of overt clinical illness. An experimental model of tolerance has been established to support this hypothesis, in that we have induced specific unresponsiveness by feeding propyl gallate to sensitized guinea pigs.
Kahn G, Phanuphak P, Claman HN. Propyl Gallate-Contact Sensitization and Orally-Induced Tolerance. Arch Dermatol. 1974;109(4):506-509. doi:10.1001/archderm.1974.01630040016003