Applications of terahertz technology in skin diseases

Terahertz (THz) waves refer to electromagnetic waves with a frequency range of 0.1-10THz and a wavelength range of 30 μm-3 mm [1] (as shown in Fig. 1). With its unique physical properties, THz technology has been widely used in aerospace, communication, medical and other fields, especially in biomedical field. The frequency range of THz waves is closely related to the rotational motion of molecules, weak hydrogen bonds, and van der Waals interactions [[2], [3], [4]]. Due to their low photon energy, THz waves do not cause significant ionizing damage to biological tissues and can be used to directly probe hydration states under physiological conditions. At THz frequencies, water exhibits a high absorption coefficient, which limits the penetration depth into biological tissues to approximately 0.2–0.3 mm. This means that only a few superficial tissues in the human body, such as the skin, cornea, and tympanic membrane, may be significantly affected by external THz radiation. Notably, the thickness of the skin is on the same order of magnitude as the wavelength of THz radiation [5,6] (see Fig. 2, which shows a schematic of the skin structure; Fig. 3, which illustrates the skin moisture content distribution).

Given that the penetration depth of THz radiation in the human body is limited to the submillimeter scale, its effects on the skin are a potential clinical concern [6]. This review aims to systematically summarize recent advances in the application of THz technology in dermatological medicine, with particular emphasis on THz detection (such as THz time-domain spectroscopy, THz-TDS) and the biological effects of THz radiation on skin tissues. We also evaluate the current understanding of safety and potential therapeutic applications, providing a foundation for future research and clinical translation.