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The aim of the study was to assess the interindividual variability of spectral remittance and spectral transmittance of visible and infrared-A radiations interacting with human skin and subcutaneous tissue, and direct measurements were taken in vivo using healthy persons of different skin color types. Up to wavelengths of about 900 nm, both spectral remittance and spectral transmittance depended significantly on the individual contents of melanin and hemoglobin in the skin, whereas the contents of water and lipids mainly determined spectral slopes of both characteristics of interaction for wavelengths above about 900 nm. In vivo measured data of spectral transmittance showed approximately similar decreases with tissue thickness between about 900 nm and 1100 nm as compared with model data which were calculated using spectral absorption and scattering coefficients of skin samples in vitro published by different authors. In addition, in vivo measured data and in vitro-based model calculations of spectral remittance were approximately comparable in this wavelength range. In contrast, systematic but individually varying differences between both methods were found for both spectral remittance and spectral transmittance at wavelengths below about 900 nm, where interaction of radiation was significantly affected by both melanin and hemoglobin. [ABSTRACT FROM AUTHOR]

Exposures of the skin with electromagnetic radiation of wavelengths between 670 nm and 1400 nm are often used as a general treatment to improve wound healing and reduce pain, for example, in chronic diabetic skin lesions. We investigated the effects of water-filtered infrared A ( wIRA) and of narrow-band IR-A provided by a light-emitting diode LED ( LED- IR-A) irradiation in vitro on 3T3 fibroblast cultures under defined conditions with and without glyoxal administration. Glyoxal triggers the formation of advanced glycation end products, thereby mimicking a diabetic metabolic state. Cell viability and apoptotic changes were determined by flow cytometry after vital staining with Annexin V, YO- PRO-1 and propidium iodide ( PI), and by SubG1 assay. Mitochondrial function and oxidative stress were examined by vital staining for radical production, mitochondrial membrane potential ( MMP) and the ratio of reduced-to-oxidized glutathione ( GSH/ GSSG). The metabolic state was monitored by a resazurin conversion assay. The numbers of apoptotic cells were reduced in cultures irradiated with wIRA or LED- IR-A. More mitochondria showed a well-polarized MMP after wIRA irradiation in glyoxal damaged cells. LED- IR-A treatment specifically restored the GSH/ GSSG ratio. The immediate positive effects of wIRA and LED- IR-A observed in living cells, particularly on mitochondria, reflect the therapeutic benefits of wIRA and LED- IR-A. [ABSTRACT FROM AUTHOR]

In many recent publications, supposed athermal effects of water-filtered infrared A (wIRA) irradiation are discussed. Those effects are mainly attributed to wavelengths in the range from 780 to 1440 nm, and should not result from warming of cellular water or any aqueous medium surrounding the irradiated sample caused by wIRA absorption. Athermal effects are considered to be induced directly by absorption of different wavelengths of the wIRA spectrum by cellular molecules or structures except water. To distinguish between thermal and athermal effects, irradiated samples have to be subjected to a very effective and precise temperature homeostasis. Any experimental effects can only be attributed to pure athermal effects, if the temperature of the irradiated samples is verifiably constant and does not result in hyperthermia. Here, data of temperature distribution in Petri dishes of different types filled with aqueous medium are presented which were estimated by model calculation for different setups of cooling. Additionally, the real temperature development was directly measured. Such a cooling unit enables long-term application of high wIRA irradiances and large doses without any detectable warming of the irradiated samples, in single cell layers. Using such a setup, thermal and athermal effects can be compared and in addition to that quantified. [ABSTRACT FROM AUTHOR]

Skin exposure to infrared (IR) radiation should be limited in terms of irradiance, exposure time and frequency in order to avoid acute or chronic damage. Recommendations aimed at protecting humans from the risks of skin exposure to IR ( e.g. ICNIRP, ACGIH) are only defined in terms of acute effects ( e.g. heat pain and cardiovascular collapse), whereas the actual exposure conditions ( e.g. spectral distribution, exposure geometry, frequency and number of exposures, thermal exchange with the environment, metabolic energy production and regulatory responses) are not taken into consideration. Since the IR component of solar radiation reaching the Earth’s surface is mainly IR-A, and considering the increased use of devices emitting artificially generated IR-A radiation, this radiation band is of special interest. A number of in vitro and/or in vivo investigations assessing cellular or tissue damage caused by IR-A radiation have been undertaken. While such studies are necessary for the development of safety recommendations, the results of measurements undertaken to examine the interaction between skin and IR radiation emitted from different sources presented in this study, together with the detailed examination of the literature reveals a wide spectrum of contradictory findings, which in some instances may be related to methodological shortcomings or fundamental errors in the application of physical and photobiological laws, thus highlighting the need for physically and photobiologically appropriate experiments. [ABSTRACT FROM AUTHOR]