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.

The human skin, as the boundary organ between the human body and the environment, is under the constant influence of free radicals (FR), both from the outside in and from the inside out. Carotenoids are known to be powerful antioxidant substances playing an essential role in the reactions of neutralization of FR (mainly reactive oxygen species ROS). Carotenoid molecules present in the tissue are capable of neutralizing several attacks of FR, especially ROS, and are then destroyed. Human skin contains carotenoids, such as α-, γ-, β-carotene, lutein, zeaxanthin, lycopene and their isomers, which serve the living cells as a protection against oxidation. Recent studies have reported the possibility to investigate carotenoids in human skin quickly and non-invasively by spectroscopic means. Results obtained from in-vivo studies on human skin have shown that carotenoids are vital components of the antioxidative protective system of the human skin and could serve as marker substances for the overall antioxidative status. Reflecting the nutritional and stress situation of volunteers, carotenoids must be administered by means of antioxidant-rich products, e.g., in the form of fruit and vegetables. Carotenoids are degraded by stress factors of any type, inter alia, sun radiation, contact with environmental hazards, illness, etc. The kinetics of the accumulation and degradation of carotenoids in the skin have been investigated.

Abstract:In the present study, the distribution of the carotenoids as a marker for the complete antioxidative potential in human skin was investigated before and after the topical application of carotenoids by in vivo Raman spectroscopy with an excitation wavelength of 785 nm. The carotenoid profile was assessed after a short term topical application in 4 healthy volunteers. In the untreated skin, the highest concentration of natural carotenoids was detected in different layers of the stratum corneum (SC) close to the skin surface. After topical application of carotenoids, an increase in the antioxidative potential in the skin could be observed. Topically applied carotenoids penetrate deep into the epidermis down to approximately 24 μm. This study supports the hypothesis that antioxidative substances are secreted via eccrine sweat glands and/or sebaceous glands to the skin surface. Subsequently they penetrate into the different layers of the SC.

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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