Contact allergy to o-cresol[mdash ]A sensitizer in phenol-formaldehyde resin

Background: In patients hypersensitive to phenol formaldehyde resin (PFR) it is, for therapeutic and preventive reasons, important to know the identity of the primary sensitizing substances, their sensitizing capacity, as well as their cross-reaction patterns. When elucidating the issue of cross reactivity in patients with contact allergy to simple methylol phenols (MP), o-cresol was shown to be a contact sensitizer. Besides cross reactivity, contamination of one or more MP(s) in o-cresol as well as o-cresol being a sensitizer of its own in PFR were possible explanations of the simultaneous positive patch test reactions to MP and o-cresol. Objective: The aim of this study was to investigate if the simultaneous allergic reactions to PFR and o-cresol could be explained by the presence of this substance in PFR. Methods: Patch testing, high-pressure liquid chromatography (HPLC), nuclear magnetic resonance spectrometry (NMR), gas chromatography (GC), and mass spectrometry (MS) were used. Results: o-Cresol was isolated from the specific PFR used in our standard patch test series and identified. The concentration in the resin was 0.066% wt/wt. Conclusion: The current study establishes o-cresol as a contact sensitizer in a PFR. The observed reactions to o-cresol could be on the basis of cross reactivity or primary sensitization.