Distribution and keratolytic effect of salicylic acid and urea in human skin.

Salicylic acid (SA) and urea are widely used in topical preparations. Using a simple tape stripping technique the effect on the binding forces within the stratum corneum and the skin absorption of SA and urea were studied. The degree of stratum corneum removal was recorded by measuring the transmission through the tape with a digital light-measuring instrument. With successive stripping of the skin the amount of tissue adhering to the tape decreased. Exposure of the upper arm to 2% SA for 6 h increased the skin material on the tape strips significantly. No significant increase was recorded after 3-hour exposure, or after exposure to 0.5% SA. Neither did the exposure to 10% urea for 3 or 6 h influence the amount of skin adhering to the tape significantly. Radiochemical analyses showed that the amount of SA and urea in each of the first 6 tape strips was about 5-15 micrograms/cm2. This technique provides a useful tool to evaluate the binding forces within the stratum corneum in relation to absorption of topically applied substances.