The benefits of the 3T3 NRU test in the safety assessment of cosmetics: long-term experience from pre-marketing testing in the Czech Republic.

We have introduced the 3T3 NRU cytotoxicity test for methodological, economical and ethical reasons as a regular part of tier pre-marketing testing to assess local tolerance of raw materials for cosmetics, household chemicals and final cosmetic products. Using the 3T3 cell line according to the standard INVITTOX protocol No.64 (NRU Assay) the borderline concentration, relevant to the highest tolerated dose, is determined for each material. The toxic effect is reached at different concentration levels specific for individual cosmetics categories, depending on their chemical characteristics. Typical ranges of cytotoxicity for specific categories of cosmetics were established after testing of hundreds of materials. The range lies between 1 microg/ml (anti-dandruff shampoos), up to 2000 microg/ml (toothpastes and mouthwashes). The 3T3 NRU cytotoxicity test is a sensitive tool able to identify more aggressive products, that are also more likely to evoke irritation in human skin. It was even possible to detect protective effects of one natural herbal ingredient. The comparative study of cytotoxicity test results and human patch test results from a group of essential oils is presented. Cytotoxicity tests represent a highly ethical approach for estimation of irritancy. On the basis of in vitro test results suggesting low risk we can proceed to confirmatory tests in human volunteers.