[Effects of peeling agents (resorcinol, crystalline sulfur, salicylic acid) on the epidermis of guinea pig (author's transl)].

The mode of action of "classical peeling agents" such as resorcinol, crystalline sulfur, and salicylic acid on the epidermis is almost unknown. There are only a few experimental data available. Therefore the effects of resorcinol, crystalline sulfur, and salicylic acid were studied. A 1% and 3% concentration of these chemicals in vaselinum flavum or Unguentum Cordes was applied to the ears and flanks of adult male guinea pigs up to 14 days. Prior to biopsies at various time intervals, 3H-thymidine was injected intradermally. Specimens were paraffin embedded and routinely processed for autoradiographical analysis. The following parameters were assessed: Labelling index (L.I. in %); number of labelled basal cells per unit length of basement membrane; papillomatosis-index; and acanthosis-factor (projection histoplanimetry). The data were statistically analysed. The peeling agents induced a concentration-dependent increase of the L.I., acanthosis, and papillomatosis. Crystalline sulfur caused the most pronounced effect, followed by resorcinol. In contrast salicylic acid caused only a minute acanthosis factor and a slight increase in labelling. The correlation coefficient r of epidermal thickness to the L.I. for all concentrations and peeling agents used reaches the high figure of 0.978 for the ear. The 1% and 3% salicylic acid has a lower acanthosis factor than vaselinum flavum by itself. Preliminary autoradiographical studies in humans with 1% and 10% salicylic acid confirm these data. Salicylic acid counteracts acanthosis. These experiments show that crystalline sulfur and resorcinol have a potent effect on cell proliferation and acanthosis. They peel via proliferation hyperkeratosis. The mode of peeling by salicylic acid must be different, as cell proliferation and acanthosis are barely enhanced. The clinically known "keratolytic" effect of salicylic acid may be due to a direct action on the intercellular cement substance of the horny cells.