Abstract

Moisturisers improve skin hydration by using humectants and/or occlusive agents. Their efficacy is investigated by monitoring skin hydration or transepidermal water loss. In-vivo measurements, however, are costly and we therefore aimed to provide equivalent skin substitute in-vitro models.
Two major models were established: collagen or synthetic membranes placed on agar-agar ‘subsurface’ gels. Their suitability for in-vitro hydration testing was evaluated by assessing their ability to accurately differentiate well-established moisturising ingredients. Second, the models were used for proof-of-concept investigations, e.g. assessing a novel active ingredient’s moisturising efficacy. Indeed, the models successfully discriminated between occlusive and emollient, as well as between formulations with different moisturising characteristics.
Taken together, each model had its strengths and weaknesses. In combination, however, such models may facilitate preliminary efficacy testing and thereby prove supportive for product development.

INTRODUCTION

Skin moisture and moisturisers

Skin moisture, or an adequate amount of water inside the outermost layers of the skin, plays a critical role in skin’s metabolism, enzyme activity, barrier function, and biophysical properties. For example, when the water content in the stratum corneum falls below a critical level, the skin becomes dry, scaly, rough, flaky, and itchy. It is also widely agreed that youthful skin retains its firmness, elasticity and smoothness, as well as other characteristics such as radiance and complexion, mainly due ... ...