RESUMO
OBJECTIVE: A mild moisturizing body wash with stearic acid, a key component of corneum lipids, and emollient soybean oil has been introduced in the market place. The objectives of this study are to determine the amount and the location of the stearic acid in the corneum after in vivo cleansing by the formulation. METHOD: Clinical cleansing studies for one and five consecutive days were carried out with the formulation containing soybean oil or petroleum jelly (PJ). The free stearic acid in it was replaced by the fully deuterated variant. The amounts of stearic acid in 10 consecutive corneum tape strips were measured by liquid chromatograph-mass spectroscopy. Separately, electron paramagnetic resonance (EPR) measurements were taken with a porcine skin after a wash by the soybean oil formulation with its free fatty acid replaced by its spin probe analogue, 5-doxyl stearic acid. RESULTS: Deuterated stearic acid was detected in all 10 consecutive layers of stratum corneum and the total amount after five washes with the soybean oil formulation was 0.33 µg/cm². The spin probe in cleanser-treated skin was incorporated in a partially ordered hydrophobic region similar to corneum lipids. The probe mobility increased in the temperature region where lipid disorder was expected. CONCLUSIONS: The estimated total fatty acid delivered to skin from cleansing is comparable to the amount of fatty acid in a corneum layer. The delivered fatty acid is most likely incorporated in the corneum lipid phase.
