Effects of all-trans retinoic acid and sodium lauryl sulphate on the permeability of human skin in vitro.

Recent in vivo investigations have shown that pretreatment with topical all-trans retinoic acid (RA) may diminish the skin response to sodium lauryl sulphate (SLS). This study evaluated the permeation of SLS through human skin after pretreatment with RA, and vice versa, by in vitro methods. The permeability coefficient of SLS (3.24 +/- 0.21 x 10(3) cm/h) and the 24-h cumulative amount of SLS (3.41 +/- 0.6% of dose applied) permeating RA-pretreated skin did not differ significantly from those across untreated skin (control) (P > 0.05). In contrast, the permeability coefficient of RA (0.23 +/- 0.05 x 10(3) cm/h) and its 24-h cumulative amount (0.37 +/- 0.05% of dose applied) penetrating SLS-pretreated skin were significantly greater than those permeating untreated skin (P < 0.05). Thus, an increase in RA penetration was induced by SLS pretreatment; however, pretreating the skin with RA did not inhibit the percutaneous permeation of SLS. Based on previous in vivo findings where RA reduced skin reactions to SLS, one would speculate that RA pretreatment may decrease SLS penetration. However, these penetration data do not necessarily uphold this presumption. Perhaps, other interactions between the substances and the skin, e.g. at cellular levels, may be responsible for the differing skin responses.