Tag Archive for: essential oils

Joint publication with dōTERRA: Skin Sensitization potency assessment of Essential Oils



Advancing Skin Sensitization potency assessment for Essential Oils

Comparative analysis of a component-based prediction model, GARDskin Dose-Response assay, and the Local Lymph Node Assay (LLNA)

A new joint article by researchers from dōTERRA and SenzaGen has been published in Toxics, providing new peer-reviewed evidence supporting the applicability of GARD®skin Dose-Response for quantitative skin sensitization potency assessment of Essential Oils, a representative class of Natural Complex Substances (NCS).

The study addresses a key gap in non-animal skin sensitization testing: the quantitative potency assessment of complex mixtures. Results demonstrate strong overall concordance between GARD®skin Dose-Response and historical LLNA data, supporting the use of New Approach Methodologies (NAMs) to derive Points of Departure (PoDs) for quantitative skin sensitization risk assessment of complex mixtures.

About the study

Eight well-studied Essential Oils were evaluated using two non-animal approaches and benchmarked against historical LLNA data:

  • GARD®skin Dose-Response: a genomics-based assay that extends the standard GARDskin OECD 442E methodology to enable quantitative skin sensitization potency assessment.
  • Component-based Prediction (CP) model: a computational approach using constituent composition and known sensitization potency data to estimate mixture potency.

Key findings:

  • Confirmed applicability of GARD®skin Dose-Response to Essential Oils for quantitative potency assessment.
  • Strong overall concordance across all three approaches, indicating comparable potency estimates.
  • GARD®-derived potency values generally aligned with historical LLNA data, supporting the method’s relevance for skin sensitization risk assessment.

Together, these findings provide further evidence supporting the use of non-animal approaches for quantitative skin sensitization risk assessment of complex mixtures. 

Dawson, Joseph T., Tim Lindberg, Prabodh Satyal, Ambika Poudel, Dakota T. Carter, Sara A. Shah, and Cécile Bascoul. 2026. 
"Comparative Analysis of Test Methods for Predicting Dermal Sensitization Potency in Essential Oils: A Component-Based Prediction Model, GARDskin Dose–Response Assay, and Local Lymph Node Assay"
Toxics 14, no. 9: 800. https://doi.org/10.3390/toxics14090800

Keywords

Skin sensitization; risk assessment; essential oils; mixtures; non-animal methods; new approach methodologies (NAMs); component-based prediction; GARDskin Dose-Response; local lymph node assay; comparative analysis


Abstract

The dose–response adaptation of the genomic allergen rapid detection for skin sensitizers (GARDskin DR) assay is a non-animal method for predicting sensitization potency. This proof-of-concept comparative analysis evaluates outputs from a component-based prediction model (CP), GARDskin DR, and historical local lymph node assays (LLNA), exploring the applicability of CP and GARDskin DR for evaluating the no-expected-sensitization induction level (NESIL) potencies of essential oils.

Eight well-studied essential oils were selected: cedarwood, cinnamon bark, clove bud, geranium, lavender, lemongrass, spearmint, and tea tree oils. Each underwent GARDskin DR as well as GC–MS, from which CP model outputs were derived. GARDskin DR, CP, and LLNA outputs were compared graphically and using preliminary descriptive statistics.

Results show overall statistical concordance in material ranking between methods (Kendall’s W = 0.857, p = 0.017). Bland–Altman log-transformed bias and limits of agreement show numerically higher NESILCP compared to corresponding NESILGARD and NESILLLNA, but sensitivity analysis shows this finding is statistically sensitive to geranium oil. Spearman’s rank correlations were significant between NESILCP vs. NESILGARD and NESILLLNA but not between NESILGARD vs. NESILLLNA despite numerical similarity.

Given the small sample, no statistical findings from this study are generalizable and should be interpreted descriptively. However, the NESIL results provide preliminary evidence supporting further evaluation of GARDskin DR and CP for dermal sensitization potency testing of essential oils.

 

Joint poster with dōTERRA: Case study on Essential Oils

Comparative analysis of skin sensitization thresholds for Essential Oils: Human, murine, and GARD®skin Dose-Response

Presented at 2025 Eurotox

Download a copy in PDF

 

Conclusion

  • NESIL predictions from GARD® were consistent with other skin sensitization data, particularly when compared to reference human data (HRIPT) and constituent predictions.
  • The assay supports quantitative skin sensitization potency assessment of complex mixtures, offering a reliable non-animal alternative to traditional testing methods.

​

Abstract

Essential oils (EOs), widely used in consumer products, require robust skin sensitization hazard and potency assessment. However, dose-response thresholds for EOs remain understudied, and current classifications under CLP mixture criteria are often overly conservative. Traditional methods, such as animal testing and human patch tests, face ethical concerns, regulatory restrictions, and reliability issues. While New Approach Methodologies (NAMs) address some of these challenges, most of them are validated only for hazard identification and lack quantitative potency assessment capabilities.

GARD®skin (OECD TG 442E) is an in vitro assay that identifies chemical skin sensitizers based on the transcriptional profiling of a 196-gene biomarker signature in the dendritic-like SenzaCell® cell line. Predictions are made using a machine-learning algorithm, which classify test chemicals as sensitizers or non-sensitizers based on the assay’s readout, Decision Values (DVs). GARD®skin Dose-Response (OECD TGP 4.106) extends this approach by evaluating test chemicals across a concentration range to establish a dose-response relationship between DVs and test chemical concentration. Sensitizing potency is quantified using cDV0, the lowest dose required to elicit a positive response in GARD®skin. Depending on the need, the readout can be used to predict LLNA EC3 values, No Expected Sensitization Induction Level (NESIL), and UN GHS/CLP classification (1A or 1B), all with high statistical significance.

This study evaluates the utility of GARD®skin Dose-Response to predict NESILs for EOs, bridging the gap between hazard identification and quantitative risk assessment. Three EOs (A, B, C) were analysed using GARD®skin Dose-Response. Their skin sensitization potency threshold levels were estimated by the assay readouts (cDV0) and NESIL predictions. Results were compared to existing murine (LLNA EC3) and human (HRIPT/HMT) data through weight-of-evidence analysis.

For test item A, the predicted NESILs spanned were 5700 (GARD®), 6900 (constituent prediction), 1800 (LLNA), 2000 (HRIPT), and 3500 µg/cm² (HMT). Test item B showed NESILs of 24000 (GARD®), 29000 (constituent prediction), 6700 (LLNA), 44000 (HRIPT), and 11000 µg/cm² (HMT). Test item C was classified as a non-sensitizer by GARD®skin Dose-Response, with constituent prediction, LLNA, HRIPT, and HMT NESILs at 20000, 3900, 20000, and 690 µg/cm², respectively.

NESIL predictions from GARD®skin Dose-Response aligned with other skin sensitization test results, supporting its utility in quantitative sensitization potency assessment of complex natural extracts like EOs. While confirmatory human studies (e.g., CNIH protocols) are recommended, this assay reduces reliance on animal and human testing and advances the use of NAMs in safety assessment.