It is currently agreed that ambient temperature influences the sebum excretion rate. By using the Sebutape technique we have confirmed this concept, which is related to an increased delivery of sebum to the surface of the skin without an increment in the number of active sebaceous follicles.

Background: Studies comparing purported antiaging compounds are rare. Objective: To compare in a randomized, placebo-controlled double-blind study 10% glycolic acid (GA), 2% 2-hydroxy-5-octanoyl benzoic acid (β-lipohydroxy acid, LSA) and 0.05% all-trans-retinoic acid (RA). Methods: Women volunteers treated one forearm twice daily with one of the active products and the other one with the vehicle. Comparative evaluations of efficacy were made using histochemistry and quantitative immunohistochemistry. Results: Improvement in the various epidermal compartments was the most prominent finding at the RA-treated site. The LSA-treated site also exhibited similar positive changes, although to a lesser degree. GA showed no significant effect. Conclusion: In the presently tested concentrations and formulations, RA had a beneficial impact upon the aging epidermis. LSA mimicked RA but with somewhat lesser efficacy. By contrast, GA appeared almost inactive.

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Topical all/trans retinoic acid (RA) has been shown to transform the horn/filled utriculi of the rhino mouse into normal follicles. We studied the early events by light and electron microscopy. Reduction in diameters of the utriculi was quantified by image analysis of whole mounts. Topical RA at 0.05% in ethanol/propylene glycol was applied daily and biopsies were taken after 1, 2, 3 and 6 days of treatment. By electron microscopy, after 3 days of RA treatment there was a great increase in the size and density of laminated membrane coating granules (MCGs) which had fused to the apical membranes of the upper granular cells. Thereafter, corneocytes within the lumina of the utriculi showed fewer desmosomes and a loss of intercellular material, accompanied by detachment from each other. Conversion to normal follicles was complete by 6 days. In whole mounts examined after 3 days of RA, there was a 75% reduction in the mean diameter of the utriculi. These results suggest that extrusion of the contents of enlarged MCGs into the intercellular corneocyte spaces facilitated separation of corneocytes, leading to rapid shedding, perhaps through the action of desmosome/lysing proteases. The conversion to normal follicles is consistent with the established role of retinoids in correcting abnormal differentiation.

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