Effects of Infrared‐A Irradiation on Skin: Discrepancies in Published Data Highlight the Need for an Exact Consideration of Physical and Photobiological Laws and Appropriate Experimental Settings

Abstract

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.

Novel Broad-Spectrum Antimicrobial Photoinactivation of In Situ Oral Biofilms by Visible Light plus Water-Filtered Infrared A

“…Interestingly, VIS ϩ wIRA triggers the production of protective proteins such as ferritin, which avert further cell damage (38). Radiators emitting VIS ϩ wIRA were found to be less painful than LED devices and extremely safe when applied with different treatment doses of up to 30 min (23,38,39). However, the moderate treatment duration of 5 min applied in our report proved to be effective and more realistic for everyday dental clinical practice.…”

“…In contrast to the common orange filter BTE 595, the fitted BTE 31 filter allowed more than a doubled weighted effective integral irradiance in terms of the absorption spectrum of protoporphyrin IX. As a result of the absorption of water molecules, the continuous water-filtered spectrum covered a wavelength range from 570 nm to 1,400 nm, with local minima at 970 nm, 1,200 nm, and 1,430 nm (23 final concentration of 100 g ml Ϫ1 . Prior to use, the freshly prepared TB and Ce6 solutions were kept in the dark at 4°C for no longer than 14 days to prevent any light-induced photochemical alterations.…”

Antimicrobial photodynamic therapy using visible light plus water-filtered infrared-A (wIRA)

“…The continuous water-filtered spectrum covers 570-1400 nm with local minima at 970 nm, 1200 nm and 1430 nm due to the absorption of water molecules (Piazena & Kelleher, 2010). The unweighted (absolute) irradiance was 200 mW cm 22 VIS+wIRA, including approximately 48 mW cm 22 VIS and 152 mW cm 22 wIRA, and the application time was 1 min.…”

“…A broad-band VIS+wIRA radiator (Hydrosun 750 FS, Hydrosun Medizintechnik) with a 7 mm water cuvette was used in this in situ assay. An orange filter, BTE31, which provides more than a doubled weighted effective integral irradiance regarding the absorption spectrum of protoporphyrin IX compared to the common orange filter BTE595, was fitted to the device.The continuous water-filtered spectrum covers 570-1400 nm with local minima at 970 nm, 1200 nm and 1430 nm due to the absorption of water molecules (Piazena & Kelleher, 2010). The unweighted (absolute) irradiance was 200 mW cm 22 VIS+wIRA, including approximately 48 mW cm 22 VIS and 152 mW cm 22 wIRA, and the application time was 1 min.…”

Multiple roles of cytochrome c oxidase in mammalian cells under action of red and IR‐A radiation

“…Nowadays the dermatologists and environmental photobiologists are interested in effects of IR-A radiation on human skin as well. It was found that this range of solar radiation could not be considered as totally non-active and innocuous but rather participating in effects of solar radiation upon human skin (6)(7)(8)(9)(10).…”