Background and Objectives: As one of the major skin fatty acids, cis-6-hexadecenoic acid (C16:1Δ6) exhibits a specific antibacterial activity and might play a specific role in the defense mechanism against Staphylococcus aureus, in healthy subjects whereas S. aureus frequently colonizes the skin of patients with atopic dermatitis (AD). Methods: Fatty acid composition of sebum at the recovery level was analyzed by gas chromatography and S. aureus colonizing the skin was assessed by the ‘cup-scrub’ method (9 patients and 10 healthy controls). To evaluate in vivo effect of C16:1Δ6 on colonization, C16:1Δ6 was applied for 2 weeks on the upper arm skin of another group of AD patients (11 patients). Results: Analysis of sebum lipids revealed that there is a significant lower free C16:1Δ6 content in nonlesional skin from AD patients compared with healthy controls. This lower content is also accompanied by a significantly lower level of C16:1Δ6 in the total fatty acid composition of sebum (analyzed following hydrolysis). The lower level of free C16:1Δ6 correlated significantly (R² = 0.41, p < 0.01) with the numbers of S. aureus colonizing nonlesional skin. Topical application of free C16:1Δ6 on the skin of AD patients for 2 weeks abolished the markedly increased bacterial count in 6 out of the 8 AD patients tested. Conclusions: Free C16:1Δ6 may be involved in the defense mechanism against S. aureus in healthy skin and this deficit triggers the susceptibility of the skin to colonization by S. aureus in AD.

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C.I. Solvent Red 23, commercial Sudan III, is widely used in cosmetic products. Chemical analyses and guinea pig sensitization tests were carried out to identify its contact allergens. In the Magnusson & Kligman guinea pig maximization test, C.I. Solvent Red 23 showed 20% positive reactions. By conducting chemical analyses with HPLC and GLC, 2-naphthol (82 ppm), azobenzene (48 ppm), Sudan I (570 ppm) and many unknown impurities, as well as the main constituent pigment Sudan III (87%), were found. The chemical structure of one unknown impurity was identified as an isomer of Sudan III. We found that purified Sudan III showed no positive reaction, while the isomer elicited 30% positive reactions, in the same guinea pig test. Furthermore, cross-sensitization with p-phenylenediamine was investigated using the guinea pig test. Animals sensitized with p-phenylenediamine also showed positive elicitation reactions with purified Sudan III. From these results, the contact allergenicity of C.I. Solvent Red 23 is considered to be due to impurities, including the isomer of Sudan III, 1-(o-phenylazophenylazo)-2-naphthol. Positive reactions to Sudan III previously demonstrated in hairdressers are due to cross-sensitivity with p-phenylenediamine.

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AND SUMMARYPyrolysis and reaction gas chromatography (GC) methods have been investigated for the homolog distribution analysis of cationic and amphoteric surfactants containing a quaternary ammonium group. Pyrolysis GC was found to be inapplicable to the analysis of amphoteric surfactants because of the formation of the nonvolatile compounds as the main products. However, when cationic and amphoteric surfactants dissolved in a 3% potassium hydroxide methanolic solution were injected into a gas chromatograph, Hofmann degradation occurred at the injection port of a gas chromatograph (reaction GC), and we obtained about the same products as were formed by the older DMF-Methylate method. Under optimum conditions, various cationic and amphoteric surfactants were degraded almost quantitatively, and the reproducibility of this method was satisfactory. Furthermore, the homolog distribution of surfactants found by the reaction GC method closely agreed with that of the starting alkyldimethylamines used. Thus, reaction GC analysis was applicable to the homolog distribution analysis of these surfactants. The reaction GC method surpassed the DMF-Methylate method with regard to the simplicity and reproducibility of the determination.