Evaluation of in vivo THz sensing for assessing human skin hydration

Hannah Lindley-Hatcher,Juan Cebrian,Emma Pickwell-MacPherson,Joseph Hardwicke,A I Hernandez-Serrano,Jiarui Wang

doi:10.1088/2515-7647/abcb71

Abstract

Terahertz (THz) in vivo reflection imaging can be used to assess the water content of the surface of the skin. This study presents the results of treating 20 subjects with aqueous, anhydrous and water-oil emulsion samples and observing the changes induced in the skin using THz sensing. These regions were also measured with a corneometer, the present gold standard for skin hydration assessment within the cosmetics industry. We find that THz sensing is effective at observing the presence of oil and water on the surface of the skin, these results can be verified with the measurements of capacitance taken by the corneometer. The THz measurements reveal a distinction between the responses of subjects with initially dry or well hydrated skin, this observation is particularly noticeable with the oil-based samples. Additionally, moderate correlation was found between the THz reflected amplitude and capacitance of untreated skin with a correlation coefficient of r = −0.66, suggesting THz sensing has promising potential for assessing skin hydration.

Highlights

Terahertz time-domain spectroscopy (THz TDS) is being studied in the context of an increasing number of biomedical applications, as its strong sensitivity to water and non-ionizing nature make it desirable for use in studying living tissues [1]
The clearest and most consistent change induced in the skin visible with both techniques is that following treatment with the aqueous sample shown in green
This study presents the first known comparison of in vivo measurements of human skin taken using THz TDS with the gold standard for skin hydration assessment, the corneometer which has known limitations

Summary

Introduction

Terahertz time-domain spectroscopy (THz TDS) is being studied in the context of an increasing number of biomedical applications, as its strong sensitivity to water and non-ionizing nature make it desirable for use in studying living tissues [1]. Ex vivo studies have shown promising results with potential for: cancer diagnosis [6] [7] [8]; quantifying the effect of different approaches to transdermal drug delivery [9]; and looking at the interactions of different moisturiser ingredients with the skin [10]. These aforementioned applications are possible due to the sensitivity of THz light to water caused by the high absorption coefficient of water at THz frequencies [11]. This restricts many in vivo studies at present to studying areas such as the skin or the eye, which can be accessed using a THz reflection system without passing through other regions of high water content

Methods

Results

Discussion

Conclusion