Irritant patch test reactions to cosmetic ingredients

Introduction
The use of cosmetics and skin care products is on a steady increase, especially in developed countries. Despite increasingly strict regulations, ingredients with irritant potential are still widely used in cosmetic products. On patch tests, irritant reactions may be mistaken for allergic reactions, leading to misdiagnoses.

Aim
To compile and analyze available data on irritant reactions to cosmetic ingredients from patch test studies in humans.

Material and methods
Data on irritant reactions to cosmetic ingredients in patch tests were extracted from published patch test studies indexed in PubMed, Embase, Web of Science or Google Scholar. The available data were pooled to assess the frequency and create a ranking list of irritant cosmetic ingredients.

Results
Data on the prevalence of irritant reactions among people undergoing patch testing (routine or experimental) were available for 47 cosmetic ingredients. Among ingredients routinely tested in the European Baseline Series, the highest rates of irritant reactions were reported for Myroxylon pereirae resin (balsam of Peru, irritant reactions in 3.40% of patch test patients), followed by Fragrance mix II (2.83%), Fragrance mix I (2.34%), colophonium (1.14%), p-phenylenediamine 1% (0.99%), hydroxyisohexyl 3-cyclohexene carboxaldehyde (0.70%), Paraben mix (0.48%) and Quaternium 15 (0.29%).

Conclusions
A range of widely used cosmetic ingredients possess irritative properties, which may contribute to irritant contact dermatitis in the consumers. In routine patch testing, irritant reactions to cosmetic ingredients may emerge in as many as one in ten patients. As irritant reactions to cosmetic ingredients in patch tests may contribute to false diagnosis of allergic contact dermatitis, doctors should be aware of the risk and able to single out such reactions.