THE SODIUM-HYDROXIDE EROSION ASSAY - A REVISION OF THE ALKALI RESISTANCE TEST

Burckhardt proposed the alkali resistance method as a means of assessi ng the integrity of the stratum corneum barrier in 1947, Researchers a fter Burckhardt largely found the test unreliable and nonreproducible; it therefore fell into disuse worldwide. We have upgraded the procedu re by exposing the skin to 1.0 M sodium hydroxide under strictly speci fied conditions for successive 1-min periods until the emergence of th e first erosions, revealed by staining with nitrazine yellow. Histolog y showed that the erosions were follicular and limited to the epidermi s, The test was highly reproducible and repeatable. We demonstrated th e usefulness of the test in the following ways: (1) the erosion time i ncreased with aging, correlating with a thickened horny layer; (2) as few as five Scotch tape strippings greatly decreased the erosion time, although transepidermal water loss was only slightly increased; (3) s light damage to the horny layer by a 24-h exposure to 0.01% sodium lau ryl sulfate sharply reduced the erosion time; (4) the erosion time dec reased after daily open applications for 3 weeks of clobetasol propion ate, corresponding to the thinned horny layer; (5) daily applications of petrolatum increased the erosion time. This new version of the alka li resistance test, renamed the sodium hydroxide erosion assay, promis es to be a useful tool for studying the horny layer barrier in healthy and diseased skin.