Attenuation total reflection (ATR) configuration offer several advantages, including (i) a larger amplitude of the reflected signal, which is less affected by strong absorption by water; (ii) a larger penetration depth of the field in the sample (the penetration depth is linear to the terahertz wavelength. The penetration depth of 0.1 THz is up to 192.1 µm). Here we analysed the following relevant factors: the contact positions between the thumb and prism, the contact pressure, the contact duration, and the material of the prism in the ATR system. Variations in skin optical properties have proved to correlate with changes in the blood glucose level.