Absorption of Fragrance Ingredients Using In Vitro Models with Human Skin

Abstract

Historically, the skin has been regarded as an inert structure which acts as a relatively impervious barrier to the inward movement of chemicals. However, it is now accepted that the skin is not a complete barrier, but is, in fact, an important route of entry of xenobiotics into the systemic circulation. The passage of a chemical from outside the skin into the body can be described as its topical fate or “life cycle”. In order to assess the risk associated with the use of fragrance chemicals, it is desirable to have knowledge concerning their “life cycle”, including the rate and extent of percutaneous absorption and the factors affecting this process. Following topical exposure to a fragrance chemical, some may be lost from the surface via the processes of evaporation, sweating, washing, abrasion and bacterial degradation. However, some maybe absorbed into the skin, the extent to which depends upon a number of factors such as the physicochemical nature of the compound in question (including its lipophilicity, octanol/water partition coefficient, volatility and molecular volume), the dose and concentration applied, the vehicle of application, the surface area and region of application, the time of skin contact, occlusion of the skin surface, the extent of skin hydration, skin temperature and the degree of skin barrier compromisation by disease or physical damage. The precise site of application is also a factor determining the rate and extent of skin absorption, as is the age of the skin and structural differences such as its thickness and the number of hair follicles.