Evaluation of in vitro testing strategies for hazard assessment of the skin sensitization potential of “real‐life” mixtures: the case of henna‐based hair coloring products containing p‐phenylenediamine

Wiley Online Library, First published: 21 April 2019,  https://doi.org/10.1111/cod.13294.

Renato I. de Ávila Danillo F. M. C. Veloso Gabriel C. Teixeira Thaisângela L. Rodrigues Tim Lindberg Malin Lindstedt Simone G. Fonseca Eliana M. Lima Marize C. Valadares


Allergic contact dermatitis reported to henna‐based hair coloring products (HPs) has been associated with adulteration of henna with p‐phenylenediamine (PPD).

To develop a testing approach based on in vitro techniques that address key events within the skin sensitization adverse outcome pathway to evaluate allergenic potential of HPs.

The following in vitro assays were used to test the sensitizing capacity of hair dye ingredients: micro‐direct peptide reactivity assay (mDPRA); HaCaT keratinocytes‐associated IL‐18 assay; U937 cell line activation test (USENS)/IL‐8 levels; blood monocyte‐derived dendritic cell test; genomic allergen rapid detection (GARD skin). Those techniques with better human concordance were selected to evaluate the allergenic potential of ten HPs.

Contrasting to the label’s information, chromatographic analyses identified PPD in all products. The main henna biomarker, lawsone, was not detected in one of 10 the products. Among the techniques evaluated by testing HDIs, mDPRA, IL‐18 assay, GARD skin and U‐SENS correlated better with human classification (concordances 91.7 to 100%) and were superior to the animal testing (concordance 78.5%). Thus, these assays were used to evaluate HPs, which were classified as skin sensitizers using different two‐out‐of‐three approaches.

Our findings highlight toxicological consequences and risks associated of the undisclosed use of PPD in henna‐based “natural” “real‐life” products.

This article is protected by copyright. All rights reserved.