A waveguide couples an acoustic source (such as an ultrasound transducer) to a custom cosmetic product (e.g., a liquid or gel-based skin care product) applied to the skin. In one exemplary embodiment, a distal surface of the waveguide is placed in contact with a relatively thin layer of skin care product that has been applied to the skin. Alternatively, the thin layer can be applied to the distal face of the waveguide, and then the waveguide placed on the skin. The custom cosmetic product has been formulated such that when ultrasound energy is directed into the custom cosmetic product via the waveguide, bubbles included or formed in the custom cosmetic product oscillate, and increase the permeability of the skin to active beneficial agents included in the custom cosmetic product.
