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Among them, the skin is primarily investigated due to the short penetration depth of THz waves caused by the high attenuation by water in biological samples. However, a complete model of skin describing the THz\u2013skin interaction is still needed. This is also fundamental to reveal the optical properties of the skin from the measured THz spectrum. It is crucial that the correct model is used, not just to ensure compatibility between different works, but more importantly to ensure the reliability of the data and conclusions. Therefore, in this review, we summarize the models applied to skin used in the THz regime, and we compare their adaptability, accuracy, and limitations. We show that most of the models attempt to extract the hydration profile inside the skin while there is also the anisotropic model that displays skin structural changes in the stratum corneum.<\/jats:p>","DOI":"10.3390\/s21113624","type":"journal-article","created":{"date-parts":[[2021,5,24]],"date-time":"2021-05-24T00:01:20Z","timestamp":1621814480000},"page":"3624","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":49,"title":["THz Sensing of Human Skin: A Review of Skin Modeling Approaches"],"prefix":"10.3390","volume":"21","author":[{"given":"Jiarui","family":"Wang","sequence":"first","affiliation":[{"name":"Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, Hong Kong 999077, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hannah","family":"Lindley-Hatcher","sequence":"additional","affiliation":[{"name":"Department of Physics, University of Warwick, Coventry CV4 7AL, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6537-0609","authenticated-orcid":false,"given":"Xuequan","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, Hong Kong 999077, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6062-5959","authenticated-orcid":false,"given":"Emma","family":"Pickwell-MacPherson","sequence":"additional","affiliation":[{"name":"Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, Hong Kong 999077, China"},{"name":"Department of Physics, University of Warwick, Coventry CV4 7AL, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2021,5,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"659","DOI":"10.1007\/BF01008897","article-title":"A model for the complex permittivity of water at frequencies below 1 THz","volume":"12","author":"Liebe","year":"1991","journal-title":"Int. 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