Application of an in vitro reconstructed human skin on cosmetics in skin irritation tests

At present, it is no longer possible to use animal testing for ingredients and cosmetic products in the Organisation for Economic Co-operation and Development (OECD) member states. However, in vitro tests are widely used to determine the safety and efficacy of ingredients and medicines.

Obviously, 3D skin models with natural human features can be used to analyze cosmetic ingredients and formulations. Skin irritation by cosmetic products is studied less than ingredients on 3D skin models. Therefore, it is necessary for us to explore using 3D skin models to detect skin irritation with resident and cleaning cosmetic products.

We used HE staining to observe the structure of reconstructed skin models, the MTT assay to analyze tissue activity, and the ELISA to detect the relative expression of IL-1α release to evaluate skin irritation with cosmetic products.

We found that 0.3% SLS treatment and 1% Triton X-100 in 3D skin models resulted in a tissue activity of <20% and increased IL-1α release. We suggest that 0.3% SLS be used as a positive control for resident cosmetics and 1% Triton X-100 be used for cleaning products. After a comprehensive analysis of the relative expression of tissue activity and IL-1α, we found that 4 cosmetic products were skin irritants. Compared with multiple skin irritation tests using rabbit irritancy evaluation, we find that skin models can objectively respond to skin irritation with reliability.

We may redefine the exposure method time for cosmetics. For resident cosmetic products, the exposure time is 18 hours. For cosmetic cleaning products, the exposure time is 1 hour, with 10% dilution. We suggest that skin irritation evaluation in 3D skin models have a tissue activity of <50% and, at the same time, have a relative expression of IL-1α that is 3-fold greater than baseline.