Effects of Temperature and Humidity on the Skin Permeation of Hydrophilic and Hydrophobic Drugs.

The humidity was a well-known method to hydrate the skin; however, the published data were varied, and systemic experiments in the previous papers were few. Therefore, the in vitro permeation of excised porcine ear skin by drugs with different polarities [aminopyrine (AMP), antipyrine (ANP), methylparaben (MP), and ibuprofen (IP)] was analyzed under a constant skin surface temperature with different temperatures and humidities to reveal the effects of temperature and humidity on the skin permeation enhancement effects. Applied formulations were prepared by mixing the drug and a hydrophilic vehicle containing glycerin. The disposition-distance profiles of water and the humectant glycerin in the stratum corneum were also investigated using confocal Raman microscopy. High absolute humidity (AH) significantly contributed to the high skin penetration of the hydrophilic penetrants AMP, ANP, and MP but not the hydrophobic penetrant IP. An increase in the partition parameter and a decrease in the diffusivity parameter occurred with an increase in AH, independent of drug polarity. Moreover, we found that dew condensation induced by high AH on temperature-controlled skin surface may effectively increase water content and may provide higher glycerin distribution in the skin barrier, the stratum corneum. Increasing the amount of water and hydrophilic vehicles such as glycerin in the stratum corneum may enhance the permeation of hydrophilic penetrants AMP, ANP, and MP. These data suggested a dew condensation on the skin surface induced by high AH at a constant skin surface temperature would be important to enhance hydrophilic penetrants.

Impact of water exposure on skin barrier permeability and ultrastructure.

BACKGROUND: Skin occlusion caused by the use of diapers or sanitary napkins often results in irritant contact dermatitis. Furthermore, prolonged occlusion and exposure to body fluids are known to increase skin hydration and permeability, thus leading to irritant contact dermatitis. OBJECTIVE: To investigate the effects of water exposure on the skin and its barrier functions, in order to obtain more insights into the mechanisms of irritant contact dermatitis. METHODS: Water patches were applied to the volar forearm skin of 10 human subjects for 3 hours. Permeability of the stratum corneum (SC) was examined with methyl nicotinate (MN). Alterations in the hydration and ultrastructure of the SC were measured with Raman spectroscopy and multiphoton microscopy, respectively. RESULTS: Water profiles found with Raman spectroscopy showed notable increases in water content throughout the SC and skin surface. Multiphoton microscopy showed morphological changes in the intercellular space of the SC. Emerged pools seemed to contribute to increased MN absorption. CONCLUSION: Excessive skin hydration leading to changes in the SC ultrastructure might result in increased skin permeability to skin irritants and allergens.