Thirty-four patients sensitive to epoxy resin were patch tested with oligomers of epoxy resin. All reacted when tested with MW 340 oligomer. Twenty-three were tested with MW 624 and MW 908 oligomers and seven with MW 1192 oligomer; none reacted. Eight patients tested with commercial mixtures of epoxy resins with an average MW 1280 and MW 1850 reacted to these resin mixtures which contained the MW 340 oligomer. The MW 340 oligomer seems to be the main ingredient responsible for contact allergy to epoxy resins in humans.

The sensitizing capacity of epoxy resins of diglycidylether-Bisphenol A type was investigated using the "guinea pig maximization test". One isolated resin had a molecular weight (MW) of 340, which is the lowest among this type of epoxy resin. The other resins were mixtures with different MWs. Their distribution is not known, but only their average MW. The low molecular weight resin sensitized all of the animals and can be classified as an extreme allergen. The sensitizing capacity decreased in inverse proportion to the increase in the average MW of the resin mixtures. The cross-testing also indicated that the resin mixtures with higher average MW contained enough of the low MW resin (MW 340) to render this resin a sensitizer. Bisphenol A did not sensitize the animals at all but epichlorhydrin sensitized 60%. It is evident that in order to formulate hypoallergenic epoxy resins it will be necessary to achieve sensitization of animals with isolated resins of varying molecular weight.

Low molecular weight oligomers of an epoxy resin of bisphenol A diglycidyl ether type were isolated by gel permeation chromatography. The sensitizing capacity of these oligomers was assessed with the "guinea pig maximization test". The oligomer with the molecular weight of 340 sensitized 80% to 100% of the animals, but produced no cross reactions to the other oligomers. The MW 624 oligomer sensitized 56-60% of the animals and 30% of these showed cross reactions to the MW 340 oligomer. The MW 908 and MW 1192 oligomers elicited no reactions. It was shown that sensitization with epoxy resin mixtures of high average molecular weight depends mainly on the content of the MW 340 oligomer.

The sensitization capacity of six epoxy reactive diluents was investigated with the "guinea pig maximization test". All the low molecular weight reactive diluents (MW 175 to 360) proved to be sensitizers. One diluent of higher molecular weight (MW 1700) produced no reaction.