The skin is the layer of flexible outer tissue covering the body and functions as an interface with the environment.^1,2 The main function of the skin is the protection from external factors, for example, against various xenobiotics and pathogens. Water and temperature balances are also regulated based on the processes in the skin. The functions and dysfunctions of the skin, including many pathological conditions, have a significant impact on both the physical health and general wellness of a person.

An increasing interest in biomedical applications of terahertz (THz) radiation, featuring the frequencies of 0.1 to 3.0 THz, the free-space wavelengths of $\simeq 3\mathrm{mm}$ to $100\mu \mathrm{m}$, or the quantum energies of $\simeq 0.3$ to 10 meV (see Fig. 1), has been observed during the past few decades,^{1 – 5} driven by rapid progress in THz technology.^6,7 Numerous research papers demonstrate the potential of THz technology in label-free early noninvasive, least-invasive, and intraoperative diagnosis of malignant and benign neoplasms with different nosologies and localizations,^{3,4,8 – 18} sensing of glycated tissues and blood in the context of diabetes diagnosis,^{1,19 – 21} determining the degree of traumatic injuries,^{22 – 25} hydration levels,^{26 – 29} and viability³⁰ of tissues. Along with the diagnostic applications, THz technology holds strong potential in therapeutics,^31,32 for example, in nonthermal regulation in expression of genes associated with cancer and inflammatory diseases.³³ Nevertheless, THz therapy is still at the initial stage of its development.

We applied terahertz (THz)-pulsed spectroscopy to study ex vivo the refractive index and absorption coefficient of human brain gliomas featuring different grades, as well as perifocal regions containing both intact and edematous tissues. Glioma samples from 26 patients were considered and analyzed according to further histological examination. In order to fix tissues for the THz measurements, we applied gelatin embedding, which allows for sustaining their THz response unaltered, as compared to that of the freshly excised tissues. We observed a statistical difference between the THz optical constants of intact tissues and gliomas of grades I to IV, while the response of edema was similar to that of tumor. The results of this paper justify a potential of THz technology in the intraoperative label-free diagnosis of human brain gliomas for ensuring the gross-total resection.

This review discusses the current state of research concerning the effects of terahertz (THz) radiation on living cells in the context of biosafety of THz radiation for the human organism.