AN ALTERNATIVE STUDY OF THE SKIN IRRITANT EFFECT OF AN HOMOLOGOUS SERIES OF SURFACTANTS

An attempt has been made to differentiate between in vivo and in vitro skin reactions to a homologous series of surfactants (sodium alkyl sulfate, R-OSO3 Na) and to determine the usefulness of percutaneous absorption in vitro as an alternative test system. Sodium alkyl sulfate showed considerable biological activity by virtue of its polar head groups. The length of the lipophilic chain in the surfactants was an important factor in their overall activity. The following in vivo tests were performed: a primary skin irritation test in guinea pigs, a primary eye irritation test in rabbits and a closed patch test in humans. Peak skin irritation occurred with C-10-C-16 sodium alkyl sulfate, which had lipophilic groups of different alkyl chain lengths. Cell injury was also evaluated by the neutral red dye uptake assay in rabbit corneal (RC) cells. C-4 and C-6 compounds had no effect, while maximal effects occurred with C-18. Protein denaturation and haemolysis occurred with C-10-C-16 compounds. In the percutaneous absorption test in guinea pig skin, permeation was low for the C-18 compound and high for the C-4 compound. The results with the C-18 compound suggest that differences between cell injury and skin irritation result from skin permeation. Although the C-18 compound caused cell injury, membrane destruction and protein denaturation were more severely with the C-10-C-16 compounds, owing to their strong haemolytic and protein-denaturation action.