Skin Structure and Penetration

Do you know how your product interacts with the skin? 
Understanding the skin structure and composition is absolutely crucial in order to predict how external chemical substances, like the ingredients in cosmetic products, might interact with the skin. The skin is designed to protect us from the environment and is structured in three main layers: the epidermis, the dermis and the subcutaneous tissue. Each layer has different types of cells – keratinocytes, melanocytes, Langerhans cells, Merkel cells, fibroblasts, mast cells, and adipocytes - with different functions. The skin attachments (hair follicles, sebaceous glands, eccrine glands, apocrine glands and nails); the cutaneous vascular system and the lymphatic and nervous systems in the dermis also play important roles. 
The hydration of the stratum corneum is achieved through two biophysical mechanisms: intercellular lipid lamellae, which provide an effective barrier to the passage of water; natural moisturizing factor, complex mixture of water soluble compounds, of low molecular weight present in the corneocytes. 

Are your active ingredients able to cross the skin barrier? How to access if the penetration of certain ingredients might increase the toxicological risk of your product? 
Despite several advantages, such as a large available surface area and relatively low enzymatic degradation, the huge barrier of the stratum corneum makes percutaneous/dermal absorption a challenge. The percutaneous/dermal absorption process describes the passage of compounds across the skin and can be divided into three steps: penetration, permeation and resorption. The three main permeation routes through the stratum corneum are: the intercellular pathway, the intracellular pathway and the follicular pathway. Several physicochemical parameters affect the skin absorption and promoters can be used to enhance the penetration of an ingredient. OECD test guideline no. 428 is a regulatory accepted alternative method to access the skin absorption of a cosmetic ingredient. 

Presented by: Marta de Oliveira Ferreira