Skin Permeation of Sunscreen Active Ingredients

Sunscreen usage has become increasingly prevalent with dermatologists pushing for consistent application and their raised concerns over skin cancer caused by harmful ultraviolet (UV) light. It is recommended that sunscreen be applied at 2 mg/cm2 leading to a total application on an average adult of ~ 2.6 grams of sunscreen. The active ingredients in many sunscreen products are organic UV filter chemicals (UVFCs) which absorb UV light and prevent skin cell damage. Some of the currently most common organic UVFCs approved for use in sunscreens by the U.S. Food and Drug Administration (FDA) are Homosalate, Octisalate, Octocrylene and Avobenzone.. After sunscreen application these UVFCs either wash off into the environment or enter the body via skin penetration. In this study, UVFC skin penetration studies are conducted using two skin models: pig skin, which is the most similar and easily accessible model to human skin, and Strat-M synthetic membranes that represent the stratum corneum or outermost layer of skin. Using a Franz cell the skin model is clamped between a donor cell, where the sunscreen is delivered, and a receptor cell filled with a phosphate buffered solution meant to mimic a physiological system. Samples are removed from the receptor cell over time and analyzed using high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS) to determine the concentration of the UVFCs within the samples. Initial studies of Homosalate skin penetration have revealed detectable but not quantifiable concentrations of Homosalate in the receiving buffer. Ongoing studies are focused on the use of LC-MS as a potentially more sensitive technique to be able to quantify the amount of Homosalate (or other UVFCs) penetrating the skin model. Longer-term experiments are also being conducted to understand the time dependance of UVFC skin penetration. Sunscreens are some of the most common over-the-counter drugs used today, and the U.S. FDA acknowledges that there is not enough scientific information about the most commonly used organic UVFCs to grant them the status of "generally recognized as safe and effective" (GRASE). Skin penetration studies are one example of additional research that is needed to make informed decisions about the active ingredients in sunscreen products.