Analysis of facial skin thickness: defining the relative thickness index.

BACKGROUND The determination of human skin thickness has been achieved through various methods, both in vivo and in vitro. Ultrasound and histometric analyses have been the most commonly used. However, absolute values of epidermal and dermal thicknesses have demonstrated variability among the different modalities, leaving questions regarding the ability to standardize or compare results of different studies. METHODS A cadaver study was designed to examine skin thicknesses in multiple anatomical sites from the same subject. Using three fresh adult cadavers, skin biopsy specimens were obtained at 15 facial sites that were identified as clinically relevant locations: upper lip vermilion, lower lip vermilion, philtral column, chin, upper eyelid, lower eyelid, brow/forehead, submental crease, right cheek, left cheek, right neck, left neck, malar eminence, nasal dorsum, and nasal tip. Histometric measurements were obtained at each location. RESULTS In all subjects, the upper eyelid had the thinnest skin and was used as the denominator to calculate relative ratios of skin thicknesses with respect to other sites of the face. Using the upper eyelid average skin thickness, the nasal tip skin thickness was 3.30 times thicker and the brow/forehead was 2.8 times thicker. CONCLUSIONS The authors propose a standardized and clinically useful method of skin thickness analysis by defining the relative thickness index. By examining relative values of skin thickness, using each subject as his or her own control, the authors demonstrated consistent ratios of dermal and epidermal thickness from one facial site to another.