An in vivo confocal Raman spectroscopic investigation of salicylic acid penetration: Variation with formulation parameters.

Salicylic acid (SA) is widely used in leave-on antiacne formulations, typically at a 2% level. As a β-hydroxy acid, it is a milder active ingredient than either α-hydroxy acids or benzoyl peroxide. SA is a keratolytic agent, a bacteriocide, and a comedolytic agent. For these reasons, improving the efficiency of SA delivery is of interest. The objective of this work is to measure in vivo SA penetration from topically applied 2% SA leave-on products and to understand the penetration in terms of formulation parameters. Penetration of SA was measured in three depth zones-0-3 μm, 3-6 μm, and 6-9 μm below the surface-using in vivo confocal Raman spectroscopy. The delivery of SA from an emulsion, pH 4.0, and a hydrogel, pH 3.75, was compared and contrasted. A comparison of depth profiles reveals, e.g., significant differences in SA distribution between-treatment profiles at various time points after treatment, particularly 3℃6 μm below the surface. The hydrogel exhibited the higher normalized level of SA in the 3-6 μm depth zone. Confocal in vivo Raman spectroscopy is proving to be a valuable tool in determination of details of penetration of products into the skin. The penetration of various 2% SA anti-acne product forms will be compared and contrasted in this presentation. Delivery of SA will be discussed in terms of formulation parameters such as phase, pH, and specific ingredients and molecular-level interactions.