The aim of the work was to determine the possibility of assessing the state of human health by the method of optical spectroscopy of skin and nail. To achieve this goal, Laser-Induced Fluorescence (LIF) spectroscopy was used. A special probe was designed, which makes it possible to record differential spectra and, as a result, to compare the shapes of spectral fluorescence lines. In vivo spectra of LIF intensities of the human finger pad and nail were measured. These spectra can be used to determine and characterize the state of human health, and it's also further monitoring in real time.When processing the spectra of different volunteers, it was found that the fluorescence spectra of the skin of physiologically healthy and pathological (in this case, type 1 and 2 diabetes) volunteers significantly differed from each other. Moreover, the analysis of these spectra makes it possible to assess the degree of pathology. It was also found that any of the three experimentally recorded fluorescence spectra is a superposition of the other two. A theoretical analysis of the multilayer model of human skin fluorescence has shown that this principle is always valid when the same chromophores are involved in fluorescence.