Resonance Raman spectroscopy was used as a fast and non-invasive optical method of measuring the absolute concentrations of beta-carotene and lycopene in living human skin.Beta-carotene and lycopene have different absorption values at 488 and 514.5 nm and, consequently, the Raman lines for beta-carotene and lycopene have different scattering efficiencies at 488 and 514.5 nm excitations. These differences were used for the determination of the concentrations of beta-carotene and lycopene. Using multiline Ar+ laser excitation, clearly distinguishable carotenoid Raman spectra can be obtained which are superimposed on a large fluorescence background. The Raman signals are characterized by two prominent Stokes lines at 1160 and 1525 cm−1, which have nearly identical relative intensities. Both substances were detected simultaneously.The Raman spectra are obtained rapidly, i.e. within about 10 s, and the required laser light exposure level is well within safety standards. The disturbance of the measurements by non-homogeneous skin pigmentation was avoided by using a relatively large measuring area of 35 mm2.It was shown that beta-carotene and lycopene distribution in human skin strongly depends upon the skin region studied and drastically changed inter-individually. Skin beta-carotene and lycopene concentrations are lower in smokers than in non-smokers and higher in the vegetarian group.

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Various fruit, vegetables and plants contain a high amount of carotenoids such as beta-carotene, lycopene, lutein, zeaxanthin, and other antioxidants in different concentrations and combinations. These substances used by nature are an effective defense mechanism against the destructive action of free radicals, which are the result of the negative influence of the environment. It was found that the peel of fruit and vegetables usually contains a higher amount of carotenoids than the pulp. Humans cannot synthesize carotenoids by itself, thus, they should be applied systemically with a supplementation rich in these substances. The diet, based on the consumption of a high amount of carotenoid rich products, increased the concentration of carotenoids in the human skin. Taking into consideration the results of previous studies, there is a strong correlation between the appearance of the skin concerning furrows and wrinkles and the level of carotenoid lycopene obtained in the skin. The present results demonstrate that a diet rich in products, which contain a high amount of carotenoids, can be an efficient strategy to reduce skin aging. In the present study, resonance Raman spectroscopy was used as a fast non-invasive optical method for the determination of the carotenoid antioxidant substances in fruit, vegetables and for the determination of the influence of a carotenoid rich diet on the antioxidant level of the human skin. Wavelength, nmAbsorption spectra of solutions of beta-carotene (solid line) and lycopene (dotted line) carotenoid antioxidant substances in ethanol

One essential reason for skin ageing is the formation of free radicals by excessive or unprotected sun exposure. Recently, free radical generation in skin has been shown to appear not only after irradiation in the UV wavelength range but also in the infrared (IR) spectral range. Sunscreens are known to protect against radicals generated by UV radiation; however, no data exist for those generated by IR radiation. This paper has investigated four different, commercially available sunscreens and one COLIPA standard with regard to radical formation in the skin after IR irradiation, using electron paramagnetic resonance spectroscopy. The use of sunscreens has led to reduced amounts of radicals compared to untreated skin. Furthermore, absorption and scattering properties and the radical protection factor of the formulations were determined to investigate their influence on the radical protection of the skin. None of these formulations contained an optical absorber in the IR range. The protection efficiency of the sunscreens was shown as being induced by the high scattering properties of the sunscreens, as well as the antioxidants contained in the formulations.

A non-invasive optical method for in vivo determination of the concentration of carotenoid antioxidant substance lycopene in the skin, based on resonance Raman spectroscopy, is presented. The Ar+ laser with an excitation wavelength at 514.5 nm was used, which corresponds to the maximum of the absorption of lycopene. This wavelength excited more lycopene than other carotenoids, because of the different absorption spectra of the carotenoids in the green spectral range. The absence of the reabsorption of carotenoids at the present wavelength and the elimination of the influences of heterogeneities of the skin, such as microstructure and pigmentation on Raman measurements by the use of a broad excitation laser beam, allows lycopene to be measured at a high accuracy. The utilization of the measurements of back reflected light from the skin allowed measurements to be performed on volunteers with all skin types.