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RIFM’s Skin Team has published two collaborative studies on the U-SENS and SENS-IS assays, adding validated options to the growing arsenal of animal-alternative methodologies used to ensure the safe use of fragrances.

For more than a decade, the Research Institute for Fragrance Materials (RIFM) has saved more than half a million animals by focusing its efforts on animal-alternative methodologies.

RIFM worked with L’Oréal and Charles River Laboratories on the U-SENS assay, a test designed to assess one of the key steps in skin sensitization, and with Procter & Gamble on the SENS-IS, a test protocol using a reconstructed human skin model in the detection of sensitizing ingredients.

Skin sensitization refers to a fragrance ingredient’s potential to cause an allergic skin reaction (such as red, bumpy, or itchy skin) in some people. As part of its ongoing Safety Assessment of individual fragrance ingredients, RIFM gauges the impact of these ingredients on the skin to determine their risk for causing skin sensitization.

Anticipating OECD’s Guideline 497: Defined Approaches on Skin Sensitisation, published last June, Dr. Isabelle Lee and RIFM colleagues, along with scientists at L’Oréal and Charles River Laboratories, compared the results of the U-SENS assay with the skin sensitization results determined by weight of evidence (WoE) from historical data available on fragrance ingredients. These data included the human Cell Line Activation Test, or h-CLAT, which OECD Guideline 497 includes. The OECD, or Organisation for Economic Co-operation and Development, comprises 38 member countries. Their Guidelines cover internationally agreed testing methods to identify potential hazards of materials, including ingredients used in fragrances. Given the study results, RIFM and its collaborators expect that the OECD will now include the U-SENS in Guideline 497 as one of the “me too” additional assays.

Assessment of the skin sensitization potential of fragrance ingredients using the U-SENS™ assay was peer-reviewed and published as a free open-access article by Elsevier’s Toxicology In Vitro.

RIFM Senior Scientist Mihwa Na and colleagues and scientists at Procter & Gamble explored the SENS-IS assay as an additional animal alternative to previous “gold-standard” assays used to determine a fragrance ingredient’s potency. It is essential to understand potency because it informs the threshold level of chemical exposure below which skin sensitization will not occur in someone who was not previously sensitized. The more potent a chemical is, the less is needed to cause an induction in skin sensitization.

Scientists categorize the potency of skin sensitizers according to their skin sensitization potential: very weak, weak, moderate, strong, and extreme. Most sensitizers fall into the “very weak” or the “weak” category.

Using a reconstructed human skin model known as EpiSkin, which simulates conditions similar to human use, the SENS-IS assay was shown to estimate the potency of fragrance materials. SENS-IS determines potency by looking at the up-regulation of the sensitization-related genes in Episkin.

Benchmarking performance of SENS-IS assay against weight of evidence skin sensitization potency categories was peer-reviewed and published in  Regulatory Toxicology and Pharmacology.