Skin tissue dielectric constant: Time of day and skin depth dependence.

Background: Skin water measurements are used to investigate skin physiology, clinically study dermatological issues, and for conditions like diabetes, oedema, and lymphedema with measurements done at various times of day (TOD). One method used is skin's tissue dielectric constant (TDC), often clinically measured to a single depth of 2.5 mm. This report characterizes intraday variations measured to multiple depths to guide expected TOD and depth dependence.

Materials and methods: Twelve medical students self-measured TDC on their forearm to depths of 0.5, 1.5, 2.5, and 5.0 mm every 2 h from 08:00 to 24:00 h on 2 consecutive days. All were trained in the procedure.

Results: TDC declined slightly from morning through evening, mostly at 0.5 mm for which TDC was reduced by 4%. TDC values were not related to participants' whole-body fat or water percentages. The TDC decrease was less at 1.5 mm where the reduction was 2.7%. At depths of 2.5 or 5.0 mm, there was no significant decrease in TOD.

Conclusion: Skin TDC shows a minor decreasing trend with an effect greater for shallower depths. In part, the clinical relevance of the findings relates to the confidence level associated with skin water estimates, based on TDC measurements, when measured at different TOD and depths during normal clinic hours. Based on the present data the TOD change is at most 4% and insignificant for measurement depths of 2.5 mm.