Use of the Skin Sandwich Technique to Probe the Role of Hair Follicles in Sonophoresis

The study used the human skin sandwich technique to investigate the effect of brief ultrasound exposure on the transfollicular pathway of hydrocortisone absorption. Without ultrasound, 46% of the drug penetration occurred through hair follicles. However, as the duration of ultrasound exposure increased, the follicular contribution dropped to zero, while total transepidermal flux significantly increased. This was attributed to the ultrasound causing the uppermost stratum corneum to slough off, which permeabilized the continuous skin surface but also plugged the hair follicle orifices.