Contact allergy to phenol-formaldehyde resins

Abstract

The raw materials, phenols and aldehydes, are not important allergens in phenol-formaldehyde resins. The strongest allergens are found among monomers and dimers with reactive hydroxymethyl groups, the hydroxymethyl phenols. Resins produced with a deficit of formaldehyde (novolac resins) show low allergenicity because they contain very low concentrations of hydroxymethyl phenols. Addition of formaldehyde needs to be done before curing. Novolac resins should not be used for patch testing. The concentrations of allergens usually drop significantly when the resins are cured (e.g., phenol-formaldehyde resin) while some resins more or less retain their levels of allergens regardless of treatment (e.g., p-tert-butylphenol-formaldehyde resin). Phenol-formaldehyde resins made from different phenols and/or aldehydes will contain different allergens and cross-reactions between different resins should not be expected. Patch testing should be performed with the specific phenol-formaldehyde resin the patient is exposed to. p-tert-Butylcatechol is a strong sensitizer used as a stabilizer in plastic monomers (e.g., styrene) and is also found in p-tert-butylphenol-formaldehyde resin. In case of a positive patch test reaction to p-tert-butylphenol-formaldehyde resin with no clinically relevant exposure to this resin p-tert-butylcatechol should be patch tested and exposure to this substance investigated.