Background. Evernia prunastri (oak moss) and Evernia furfuracea (tree moss) are lichens from which natural extracts are obtained.
Objectives. To identify possible subgroups of E. furfuracea-sensitized patients according to whether these are allergic to lichen components or to contaminants.
Methods. A retrospective analysis was performed of surveillance data collected by the Information Network of Departments of Dermatology (www.ivkd.org) in 2003–2010 with oak moss absolute (1% pet.), tree moss absolute (1% pet.), and colophonium (colophony, 20% pet.).
Results. In total, 3030 patients had been tested with all three allergens. Positive reactions to E. furfuracea were observed in 6.37%, to E. prunastri in 5.71%, and to colophonium in 4.82%. Concordance between positive reactions to E. prunastri and E. furfuracea was good only in patients not co-sensitized to colophonium (Cohen's κ = 0.681, 95% confidence interval 0.615-0.746). Moreover, E. furfuracea-sensitized patients showed (strong or extreme) concomitant reactions to colophonium significantly more often if not co-sensitized to E. prunastri.
Conclusions. Two subgroups of E. furfuracea-sensitized patients are identifiable: (i) those with sensitization to (oxidized) resin acids, as indicated by positive patch test reactions also to colophonium, and (ii) those non-sensitized to resin acids, but sensitized to common constituents of E. prunastri and E. furfuracea.