Interactions between the stratum corneum and topically applied products: regulatory, instrumental and formulation issues with focus on moisturizers

Abstract

Virtually everyone in Europe will use at least one cosmetic product every day. The extensive use of cosmetics and results from measurements of quality of life in patients with skin diseases demonstrate the importance of a healthy skin. The skin is not only a barrier against desiccation and intrusion of harmful materials, but also an organ of social communication, where dry, scaly, rough stratum corneum is unappealing to touch, inducing anxiety and depression. Knowledge about the skin biochemistry and the use of noninvasive instruments facilitate the development of topical products and quantification of their effects. The presentation of the products and mode of action determine the regulatory demands and the approval process, as they can fall into different regulatory entities, such as cosmetics, medicinal products, medical devices and as other chemical products. The majority of the topical products on the market are regulated as cosmetics. For example, facial skin care and daily moisturizing routines are frequently used. However, despite visible relief of dryness symptoms, some products are reported to result in deterioration of the skin barrier function. New clinical outcomes show important clinical differences between formulations and the relapse of eczema. In a worst case scenario, treatment with a moisturizing cream may increase the risks of eczema and asthma. In the present overview, product presentations and mode of actions are reflected against the regulatory demands in Europe. The regulations are continuously revisited and new guidelines are being implemented, such as the new cosmetic regulation with advice on testing and responsible marketing.