The skin compatibility of distilled tall oils: evaluation with the bovine udder skin in vitro model system.

Distilled tall oil (DTO) is a natural product, often added as an emulsifying ingredient in cutting fluids used as lubricants and coolants in metal working. The in vitro model used to test the skin compatibility of these substances, was the isolated perfused ex vivo bovine udder skin (BUS) model. After three exposure periods (0.5, 1, and 5 hours), cytotoxic effects were determined by using the 3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and tissue levels of the pre-inflammatory mediator prostaglandin E2 (PGE2) in treated whole skin biopsies were assessed by using an enzyme immunoassay. The BUS standard study design, involving a single application, was previously developed to investigate the skin irritation potential of cosmetics and chemicals. In the current study, four different batches of undiluted DTO, and tall oil fatty acids as a reference compound, were applied both singly and repeatedly (three times), under open conditions which were in line with the potential usage conditions in the work place. Under the standardised single application conditions, no major differences in cytotoxic effects or PGE2 levels between the samples were apparent, so no indication of a skin irritation potential could be concluded. This result is in accordance with prior in vivo studies for acute dermal toxicity. Under repeated application conditions, signs of cytotoxicity were observed after the application of one of the DTO samples, which was known to be derived from different raw materials. Therefore, it was concluded that, generally, the presence of DTO at a concentration of up to 10% in cutting fluids, is not expected to result in any DTO-related deterioration of the skin.