8 alkyl gallates, including the widely used antioxidants propyl, octyl, and dodecyl (= lauryl) gallate, have been subjected to experimental sensitization in guinea pigs. Using a modern sensitization procedure, the results showed that all gallates are moderate to strong contact sensitizers: dodecyl (= lauryl) gallate was found to be the strongest. A characteristic correlation between side chain length and mean response was observed, giving a maximum of sensitization at a length of 12 carbon atoms (dodecyl gallate). A literature review revealed that the frequency of reports of allergic contact dermatitis from antioxidants of the gallate type has increased in the last 4 years. In most cases, the moderate sensitizer propyl gallate was the source of sensitization.