DIFFERENTIAL IRRITANT SKIN-RESPONSES TO TANDEM APPLICATION OF TOPICALRETINOIC ACID AND SODIUM LAURYL SULFATE .2. EFFECT OF TIME BETWEEN FIRST AND 2ND EXPOSURE

In clinical practice, the cutaneous exposure to chemical irritants suc h as surfactants and topical drugs is frequent, Topical all-trans reti noic acid (RA) is often associated with irritation and induces epiderm al changes similar to those produced by sodium lauryl sulphate (SLS), Using bioengineering techniques, e.g. assessing transepidermal water l oss (TEWL), capacitance and chromametry, we investigated the variation s of the skin response to SLS and RA and to both chemicals applied seq uentially, allowing different time periods (from 1 h to 2 weeks) betwe en applications of SLS and RA, Both chemicals caused irritation as ass essed by visual scoring, but the values from the objective variables d iffered at different time periods. TEWL increased dramatically shortly after applying SLS but the increase was delayed after RA. After apply ing SLS, the capacitance generally decreased then returned to basal va lues; treatment with RA produced an overall increase. Only the results from chromametry were similar, After tandem application, the drugs we re synergistic for all variables except capacitance, showing an antago nistic interaction for skin hydration. These results suggest that non- specific skin irritation profoundly reflects different mechanisms of a ction at tissue level, With sequential application, SLS injury modifie d the response to RA for at least 1 week after applying SLS. These lat e effects of detergents should be considered when studying irritant ch emical interactions and in developing strategies for the management of occupational and other irritant dermatitis.