A Raman spectrum is measured inside animal tissue, such us human skin tissue, at a selected depth from a surface the tissue. A pH value is computed using a function that assigns a pH value as a function of the measured Raman spectrum. The computation may involve computing a number representing a ratio of concentrations of a protonated and a deprotonated version of a chemical substance from the Raman spectrum and generating pH information on the basis of said number. The chemical substance is for example a form of Urocanic acid (UCA). UV exposure is measured from the weight of the spectrum of cis-UCA.