IN-VIVO HUMAN SKIN BARRIER MODULATION BY TOPICAL APPLICATION OF FATTY-ACIDS

The in vivo effects of fatty acids on skin barrier function were asses sed by measuring: (i) transepidermal water loss (TEWL), (ii) diffusion lag times for hexyl nicotinate (HN), and (iii) irritant skin response using laser Doppler velocimetry (LDV) in combination with visual scor ing, Two classes of fatty acids have been investigated: straight-chain saturated fatty acids (SFA), having 6-12 carbon atoms, and unsaturate d fatty acids (UFA): oleic, linoleic, a-linolenic and arachidonic acid s. It has been reported that these acids can enhance the permeation of various compounds across the skin. After topical and occlusive applic ation as a solution in propylene glycol (PG) for 3 h on the volar arm of human subjects, SFA only caused a slight irritation and increase in TEWL, The diffusion lag times of HN were reduced by the application S FA to the same extent as and not more than by the application of the p ure solvent PG, In contrast, the application of UFA caused a significa nt increase in TEWL and LDV (irritation) responses. The TEWL values af ter oleic acid application were higher than those observed for the oth er three acids, while the irritation potential of arachidonic acid was the highest among UFA, As with SFA, sites treated with UFA did not sh ow significantly different lag times of HN diffusion from PC-treated s ites, The data suggest that the degree of irritation and the degree of barrier modulation for fatty acids an not necessarily correlated.