Contact Allergy to Epoxy Resins of the Bisphenol F-type

Epoxy resins based on bisphenol A are well-known contact allergens and often cause occupational contact allergy. The most important allergen is the monomer diglycidyl ether of bisphenol A (DGEBA). Epoxy resins of the bisphenol F-type contain 3 isomers of the diglycidyl ether of bisphenol F; p,p'-DGEBF, o,p'-DGEBF, and o,o'-DGEBF, whereas epoxy resin(s) based on bisphenol A (DGEBA-R) contain virtually only 1 isomer of DGEBA. The allergenicity of DGEBA has been investigated earlier, but the DGEBF isomers have not previously been investigated as contact allergens. When an epoxy resin based on bisphenol F was inserted in the standard patch test series of our department, it was found that contact allergy to this type of epoxy resin was at least as common as contact allergy to DGEBA-R. A majority of the patients reacted to both types of epoxy resins. Both p,p'-DGEBF and o,p'-DGEBF were shown to be sensitizers in humans, while o,o'-DGEBF elicited surprisingly few reactions. p,p'-DGEBF was found to be a sensitizer and at least as strong as DGEBA. All 3 DGEBF isomers were found to be strong sensitizers in animal studies. It was also found that DGEBA, p,p'-DGEBF and o,p'-DGEBF cross-reacted with one another to a high degree, while o,o'-DGEBF did not. o,o'-DGEBF was assumed to be a sensitizer mainly in the absence of the other 3 substances. Humans are then generally not sensitized to o,o'-DGEBF, since it does not occur alone in the epoxy resins of the bisphenol F-type. For the individuals with contact allergy both to DGEBA-R and epoxy resins of the bisphenol F-type, concomitant sensitization as well as cross-sensitization might be the case. When contact allergy to epoxy resins of the bisphenol F-type is suspected, this type of epoxy resin should be patch tested, especially if the DGEBA-R patch test is negative. Depending on the clinical situation, the patch-test concentration recommended is 0.25-0.5%. Consecutive patch testing with epoxy resins of the bisphenol F-type at a concentration of 1.0% is not recommended due to the possibility of patch-test sensitization. It was found that the sensitivity of the thin-layer chromatography method was around 200 times more sensitive for DGEBA than for DGEBF isomers. In patients with contact allergy to DGEBA-R, the cause of allergic contact dermatitis might be an epoxy resin of the bisphenol F-type. The latter resins are most probably not detected by the TLC method developed for DGEBA-R. If the product is analyzed only with the TLC method, the relevance of the contact allergy to DGEBA-R might therefore remain unrecognized. In an industrial investigation among 603 workers exposed to epoxy resins 20.3% of the 325 patch-tested workers had occupational ACD. Approximately 15% of the workers with occupational ACD had contact allergy to DGEBA-R and 36% had contact allergy both to epoxy resins of the bisphenol F-type and DGEBA-R. Around 40% of the patch-tested workers were estimated to have skin disease either caused or aggravated by work. Although a well-known occupational contact allergen, a high frequency of contact allergy to DGEBA-R among exposed workers was found. Thorough instruction concerning protection, most importantly for new employees, as well as the development of production methods that minimize exposure, especially to DGEBA-R, are necessary measures for preventing occupational dermatoses among workers exposed to ERS in the manufacture of rotor blades for wind turbines.