Test materials that absorb light in the UVB, UVA, and visible light range and are topically applied to or may be distributed to sun exposed areas of the skin should be considered for photosafety evaluation. Test materials that are phototoxic can produce adverse effects in the presence of light after exposure.
At IIVS, we perform two in vitro assays that are routinely used to evaluate phototoxicity hazard and risk. The 3T3 Neutral Red Uptake (NRU) Phototoxicity Assay (OECD Test Guideline 432) is a monolayer cell-based assay used to assess phototoxicity of test materials that may be systemically administered or those that may be part of formulations intended for topical exposure to the skin (e.g., botanicals, drug intermediates, and ingredients). The 3-dimensional Reconstructed human EpiDermis (RhE) Assay utilizes a dermal model containing differentiated cells and functional stratum corneum to assess photosafety of a greater variety of test materials, including final formulations and insoluble materials. These assays can be used independently or as part of a tiered testing strategy.
Test materials are administered to their respective test system and exposed in the presence and absence of light. Viability is calculated from the light and dark-exposed cells or tissues, and the differences, if any, in viability are used to assess phototoxicity potential.
The following images are representative images of each in vitro assay and the solar simulator used to produce the photoirridiation: