of the epidermal layer of skin and the penetration depth of the incident light the stratum corneum hydration measurement is therefore suitable for further spectral analysis and the quantification of biological and chemical compounds such as blood analytes application_number US 16119702 A description the system for quantifying the stratum corneum hydration non invasively provides an apparatus for measuring the near infrared absorption by tissue irradiated with near infrared energy and a procedure for determining hydration of the stratum corneum although the invented apparatus and procedure are described herein with respect to quantifying hydration of the stratum corneum one skilled in the art will recognize that the invention has application in quantifying hydration of other forms of tissue the apparatus includes an energy source 11 one or more sensor elements an interface 12 to the subject 10 a wavelength selection device and an analyzer the source generates and transmits near infrared energy in the wavelength range 700 2500 nanometers and consists of a device such as an led array 11 or a quartz halogen lamp the sensing elements are detectors 14 which are responsive to the targeted wavelengths the method of wavelength separation includes a monochromator an interferometer or successive illumination through the elements of an led array 11 the interface to the subject comprises a means of transmitting energy from the source 11 to the target.