Predicting the Rate and Extent of Fragrance Chemical Absorption into and through the Skin

The absorption of a chemical into the skin depends upon its physicochemical properties, the manner in which it is presented to the skin (i.e., the "vehicle" in which it is applied.), the "skin environment", and the duration of exposure (t(exp)). There is value, therefore, in attempting to quantify the maximum percutaneous penetration of a chemical and then using this characteristic to evaluate exposure based upon the specific scenario involved (for example, when the chemical and/or the principal vehicle constituents are volatile). Chemicals may be classified by their maximum, theoretically calculated fluxes (J(max)), and the quantity (Q) absorbed per exposure may then be calculated from Q = J(max)t(exp)A, where A is the area of skin contact. This approach is conservative and assumes that (i) the compound is applied at its saturation concentration and (ii) no depletion of chemical from the applied phase occurs during t(exp). For a number of fragrance chemicals, agreement between predicted and experimental results for this extreme scenario is good. On the other hand, for smaller, finite "doses'', particularly of highly volatile chemicals, theory largely overpredicts reality. A refined, "finite dose" model is therefore required to account for surface depletion due to skin uptake and/or evaporative loss.