In-vivo Skin Hydration Sensing Using a Hand-Held THz Scanner

Terahertz (THz) light is a potentially powerful tool for medical applications in non-invasive tests [1]. This is primarily due to the strong interaction of water molecules present in biological agents. Additionally, the energy of THz photons (4.14 meV at 1 THz) is much lower than the energy necessary to impose any changes in the DNA, resulting in a safe technique. However, the strong absorption of water (200
$cm^{-1}$
at 1 THz) prevents THz radiation from penetrating further than few tens of microns into living skin, limiting this technique to the evaluation of epithelial tissues such as the skin. Since the early 2000's it has been suggested that THz light could be employed to inspect skin cancer evolution, as such disease is well known for changing the water levels of the affected areas [2]. Unfortunately, commercially available pulsed THz spectrometers are not designed to be used for medical applications. Using our own home-built hand-held THz scanner, we successfully measured the hydration dynamics and thickness of the most external layer of skin; the stratum corneum (SC) of 95 healthy volunteers.