In vivo quantitative analysis of the effect of hydration (immersion and Vaseline treatment) in skin layers using high-resolution MRI and magnetisation transfer contrast*

Background/aims: Many claims are made as to the efficacy of topical preparations in moisturising the skin, yet most of these claims cannot be substantiated by scientific study for the skin layers beneath the stratum corneum, and yield no information on the remainder of the epidermis and dermis. This argues for an in vivo quantitative method for measuring the effect of water loading extended to various layers of the skin. Methods: Detailed high-resolution in vivo MRI studies of hydration and dehydration of finger pad skin layers were conducted on one normal subject using two moisturisation methods (topical white soft paraffin (Vaseline) and water immersion). The dehydration study was carried out immediately following removal from prolonged skin moisturisation. Inter-individual variability for skin hydration (group study) was studied in seven healthy volunteers at 0 and 7 h hydration with Vaseline. Location dependence in skin hydration was investigated on the same subject by looking into the hydration of forearm and finger pad skin. System stability and measurement reproducibility was verified through a detailed phantom study. Results: Images of normal and hydrated human skin were obtained in vivo at voxel dimensions of 50 μm×150 μm×1000 μm. The effect of hydration and dehydration as a function of exposure to moisturiser (i.e. water and Vaseline) on the image signal intensity, observed T1, and interaction of free and bound water in specific tissues were identified and correlated with existing physiological knowledge. Swelling of stratum corneum due to hydration was expressed as an in vivo model of tissue hydration. Conclusion: Results of the dehydration study showed that the changes due to the previous hydration of the skin are reversible for all skin layers. For both moisturisation methods (i.e. Vaseline and skin bathing), the effects of hydration and dehydration on the skin were similar. The trends of the MRI parameters for finger pad and arm skin were similar. The group study showed low inter-subject variability of hydration on stratum corneum and epidermis.