Source: Okayama University (JAPAN), Public Relations Division
For immediate release: 20 October 2022
Okayama University research: The skin electrically modelled

(Okayama, 20 October) Researchers at Okayama University report in Advanced Biomedical Engineering a practical method to measure the thickness and the water content of the outermost layer of the human skin. These are important quantities in the context of understanding and monitoring the skin’s barrier function.

The outermost layer of the human skin, called the stratum corneum, protects the body against potentially dangerous substances. But for the stratum corneum to function properly as a barrier, it has to have a certain thickness and a certain water content. Measuring these by conventional methods, however, is time-consuming and not practical. Now, Professor NAKAMURA Takao, Assistant Professor KUSUHARA Toshimasa from Okayama University, UEHARA Osamu from ALCARE Co., Ltd. and colleagues have developed a simple method to estimate the thickness and the water content of the stratum corneum. The method, relying on an electrical-circuit model of the skin, is expected to help detect skin barrier function deterioration, which can cause allergies or skin conditions.

The researchers based their approach on the notion that the stratum corneum has a particular electric response — it ‘resists’ an electrical current. They modelled the outer skin layer as an electrical component: a resistance (R) and a capacitance (C) placed in parallel. The numerical values of R and C depend on the thickness and the water content of the stratum corneum; Professor NAKAMURA and colleagues proposed mathematical formulas describing this dependence. These formulas were then used to obtain expressions of thickness and water content as a function of R and C.

The scientists developed a practical device that, by holding it against the skin of the forearm, provides values of the electrical impedance of the skin, which can be easily converted into values of R and C. (The electrical impedance is the ‘opposition’ of a circuit component to an applied alternating current.) These estimates for R and C could then be used for calculating thickness and water content by means of the established mathematical relationships between them.

Professor NAKAMURA and colleagues then tested how well the impedance-based estimates compared to values of thickness and water content directly measured using conventional (but non-practical) methods called confocal laser microscopy and confocal Raman spectroscopy, respectively. They performed skin measurements on 16 individuals. Impedances were measured for two alternating-current frequencies (500 Hz and 100 kHz). Statistical analyses of the comparisons between estimates and conventional measurements showed good agreement: the correlation coefficients were 0.931 and 0.776 for thickness and water content, respectively. (The closer a correlation coefficient is to 1, the better the agreement.) To explain the deviations, the scientists suggest that measurements of the skin electrical impedance may be influenced by several factors, including measurement time and sweat on the skin.

Measurements on an increased number of participants are necessary to confirm the results of the current study. Nevertheless, quoting the researchers, “it is … expected that the [resistance–capacitance] model can be used as a simple model capturing the state of the stratum corneum”.


Background
The stratum corneum is the outermost layer of the human skin. It is formed by dead tissue and has protective and regulatory functions, including impact resistance, hydration regulation, and blocking of toxic substances, irritants and allergens. It functions as a barrier, shielding underlying cells from mechanical stress, infection, and harmful chemicals.

Qualitatively characterizing the stratum corneum is important for understanding and checking its barrier function. Specifically, its thickness and its water content are two relevant parameters; measuring them, however, is not easy. Professor NAKAMURA Takao, Assistant Professor KUSUHARA Toshimasa from Okayama University, UEHARA Osamu from ALCARE Co., Ltd. and colleagues have now developed a practical method to measure these two quantities. The method is based on measuring electric impedances of the skin by means of an easy-to-use device held against the forearm. By modelling the stratum corneum as a simple electrical circuit consisting of a resistance and a capacitance placed in parallel, estimates for its thickness and its water content can be calculated using formulas involving the measured impedances.

Reference
Osamu Uehara, Toshimasa Kusuhara, Kenichi Matsuzaki, Yoshitake Yamamoto, Takao 　Nakamura. Skin electrical impedance model for evaluation of the thickness and water content of the stratum corneum. Advanced Biomedical Engineering, Vol. 11, p.98-108, 2022.
DOI：https://doi.org/10.14326/abe.11.98
https://abe-journal.org/issues/2022/04/27/682

Correspondence to
Professor NAKAMURA Takao, Ph.D.
Department of Radiological Technology,
Graduate School of Health Sciences, Okayama University,
2–5–1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
E-mail: nakamura (a) md.okayama-u.ac.jp
For inquiries, please contact us by replacing (a) with the @
https://www.cc.okayama-u.ac.jp/~nakamura/index.html

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