The effect of three common emulsifiers and some fatty components of dermatological vehicles on transepidermal water loss (TEWL) and on percutaneous penetration was studied. The emulsifiers tested were 20% cetostearol in ethanol, 20% sorbitan sesquioleate in ethanol and 2% glycerol monostearate in chloroform. The oily components were jojoba oil and Ceridal skin oil (Rhone Poulenc) undiluted and 2% cholesterol in ether. The test substances were applied twice daily on the back skin of the subjects for 3–7 days. Cetostearol increased TEWL in both atopic and non-atopic subjects. Sorbitan sesquioleate did the same in non-atopics but not in atopics. The other substances tested did not influence TEWL significantly. In the non-immunological contact urticaria (NICU) test with 250 mM benzoic acid (BA), the non-atopics, but not the atopics, showed significantly stronger reactions in the areas treated with sorbitan sesquioleate than in other test areas. In another study, the emulsifiers and cholesterol were mixed with petrolatum at a ratio of 20:80. These mixtures did not alter TEWL, nor did they increase the skin reaction to BA in the NICU test. The results suggest that, of the many components of dermatological vehicles, at least cetostearol and sorbitan sesquioleate may influence the barrier function of the stratum corneum.