Assessing Facial Skin Hydration via Tissue Dielectric Constant (TDC): Suitability of Single Versus Multiple...

Noninvasive tissue dielectric constant (TDC) measurements provide a useful index of local skin water because TDC, measured at 300 MHz, depends directly on the amount of free and bound water in the measurement volume. Since the hydration status of facial skin is a fundamental factor affecting multiple dermatological conditions, including rosacea, psoriasis, and eczema, TDC values may be useful for assessing dermal hydration in these conditions. Although some data on female facial values have been reported, data on male facial TDC are quite limited. Further, since multiple skin sites often need to be evaluated, time constraints in the clinic may limit the acquisition of useful data if multiple measurements are required at each site. Thus, the study's goal was to determine if a single TDC measurement, rather than averaging multiple measurements, would be sufficient.  Methods: TDC was measured in triplicate bilaterally at the forehead (F), cheek (C), and jowl (J) areas to an effective depth of 1.5 mm in 40 male subjects while they were supine and then seated after 15 minutes at each position. The first TDC value (TDC1) was compared with the average of the first and second (TDC12) and with the triplicate average (TDC123).

Group-average TDC values did not differ statistically among TDC1, TDC12, and TDC123 at any facial site, whether measured with the subject supine or seated. Supine TDC1 values (mean ± SD) for the F, C, and J areas were 42.11 ± 3.19, 39.15 ± 5.49, and 43.44 ± 4.56, respectively. The corresponding TDC values with subjects seated were 40.68 ± 2.99, 38.49 ± 5.54, and 41.97 ± 4.37. Supine-seated differences were statistically significant at the forehead and jowl areas (p < 0.001) but not at the C (p = 0.193). TDC differences among sites, though small, were statistically significant (p < 0.001) at both positions. C had the lowest TDC value. On an individual basis, no subject had a TDC1 value that differed by more than 3% from the triplicate average.

Results indicate that when clinical time is a concern, or when experimental time needs to be shortened for any reason, accurate facial TDC data may be obtained at the F, C, and J areas using a single TDC measurement with the subject either supine or sitting, whichever is appropriate for the patient and examiner.