Optical methods for noninvasive determination of carotenoids in human and animal skin

Carotenoids are important substances for human skin due to their powerful antioxidant properties in reaction of neutralization of free radicals and especially reactive oxygen species, including singlet oxygen. Concentration of carotenoids in the skin could mirror the current redox status of the skin and should be investigated in vivo. Optical methods are ideally suited for determination of carotenoids in mammalian skin in vivo as they are both noninvasive and quick. Four different optical methods could be used for in vivo measurement of carotenoids in the human or animal skin: (1) resonance Raman spectroscopy; (2) Raman microscopy; (3) reflection spectroscopy; (4) skin color measurements. The advantages, shortcomings, and limitations of the above-mentioned optical methods are discussed.