Assessment of the skin sensitization potential of fragrance ingredients using the U-SENS™ assay

Toxicol In Vitro. 2022 Mar:79:105298. doi: 10.1016/j.tiv.2021.105298. Epub 2021 Dec 11.


The U-SENS™ assay was developed to address the third key event of the skin sensitization adverse outcome pathway (AOP) and is described in OECD test guideline 442E, Annex II. A dataset of 68 fragrance ingredients comprised of 7 non-sensitizers and 61 sensitizers was tested in the U-SENS™ assay. The potential for fragrance ingredients to activate dendritic cells, measured by U-SENS™, was compared to the sensitization potential determined by weight of evidence (WoE) from historical data. Of the non-sensitizers, 4 induced CD86 cell surface marker ≥1.5-fold while 3 did not. Of the sensitizers, 50 were predicted to be positive in U-SENS™, while the remaining 11 were negative. Positive and negative predictive values (PPV and NPV) of U-SENS™ were 93% and 21%, respectively. No specific chemical property evaluated could account for misclassified ingredients. Assessment of parent and metabolite protein binding alerts in silico suggests that parent chemical metabolism may play a role in CD86 activation in U-SENS™. Combining the U-SENS™ assay in a "2 out of 3" defined approach with the direct peptide reactivity assay (DPRA) and KeratinoSens™ predicted sensitization hazard with PPV and NPV of 97% and 24%, respectively. Combining complementary in silico and in vitro methods to the U-SENS™ assay should be integrated to define the hazard classification of fragrance ingredients, since a single NAM cannot replace animal-based methods.

Keywords: Fragrance allergy; Key event 3; New approach methodologies (NAMs); OECD TG 442E; Skin sensitization; Skin sensitization AOP; U-SENS™.

MeSH terms

  • Allergens
  • Animal Testing Alternatives
  • Humans
  • Perfume / toxicity*
  • Predictive Value of Tests*
  • Toxicity Tests / methods*
  • U937 Cells


  • Allergens
  • Perfume