K Levi1, A Kwan, A S Rhines, M Gorcea, D J Moore, R H Dauskardt. 1. Department of Materials Science and Engineering, 496 Lomita Mall, Durand Building, Room 121, Stanford University, Stanford, CA 94305-2205, USA.
Abstract
BACKGROUND: Emollient molecules are widely used in skin care formulations to improve skin sensory properties and to alleviate dry skin but little is understood regarding their effects on skin biomechanical properties. OBJECTIVES: To investigate the effects of emollient molecules on drying stresses in human stratum corneum (SC) and how these stresses are related to SC components and moisture content. METHODS: The substrate curvature method was used to measure the drying stresses in isolated SC following exposure to selected emollient molecules. While SC stresses measured using this method have the same biaxial in vivo stress state and moisture exchange with the environment, a limitation of the method is that moisture cannot be replenished by the underlying skin layers. This provides an opportunity to study the direct effects of emollient treatments on the moisture content and the components of the SC. Attenuated total reflectance Fourier transform infrared spectroscopy was used to determine the effects of emollient molecules on SC lipid extraction and conformation. Results Emollient molecules resulted in a complex SC drying stress profile where stresses increased rapidly to peak values and then gradually decreased to significantly lower values compared with the control. The partially occlusive treatments also penetrated into the SC where they caused extraction and changes in lipid conformation. These effects together with their effects on SC moisture content are used to rationalize the drying stress profiles. CONCLUSIONS: Emollient molecules have dramatic effects on SC drying stresses that are related to their effects on intercellular lipids and SC moisture content.
BACKGROUND: Emollient molecules are widely used in skin care formulations to improve skin sensory properties and to alleviate dry skin but little is understood regarding their effects on skin biomechanical properties. OBJECTIVES: To investigate the effects of emollient molecules on drying stresses in human stratum corneum (SC) and how these stresses are related to SC components and moisture content. METHODS: The substrate curvature method was used to measure the drying stresses in isolated SC following exposure to selected emollient molecules. While SC stresses measured using this method have the same biaxial in vivo stress state and moisture exchange with the environment, a limitation of the method is that moisture cannot be replenished by the underlying skin layers. This provides an opportunity to study the direct effects of emollient treatments on the moisture content and the components of the SC. Attenuated total reflectance Fourier transform infrared spectroscopy was used to determine the effects of emollient molecules on SC lipid extraction and conformation. Results Emollient molecules resulted in a complex SC drying stress profile where stresses increased rapidly to peak values and then gradually decreased to significantly lower values compared with the control. The partially occlusive treatments also penetrated into the SC where they caused extraction and changes in lipid conformation. These effects together with their effects on SC moisture content are used to rationalize the drying stress profiles. CONCLUSIONS: Emollient molecules have dramatic effects on SC drying stresses that are related to their effects on intercellular lipids and SC moisture content.