Combined, Simultaneous Exposure to Radiation Within and Beyond the UV Spectrum: A Novel Approach to Better Understand Sk
The effects of UVB and UVA radiation on human skin have been extensively studied, and as one consequence, sunscreen products usually provide protection against both radiation types. There is now also compelling evidence that nonionizing radiation which is
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Combined, Simultaneous Exposure to Radiation Within and Beyond the UV Spectrum: A Novel Approach to Better Understand Skin Damage by Natural Sunlight Jean Krutmann, Kevin Sondenheimer, Susanne Grether-Beck, and Thomas Haarmann-Stemmann
2.1
Introduction
One of the major threats to human skin health is natural sunlight. There is no doubt that chronic exposure to ultraviolet B (290–320 nm, UVB) radiation is the major cause for nonmelanoma skin cancer in humans, as reviewed extensively in Chap. 7 of this monograph. It is now also well established that longer UV radiation, i.e., UVA (320–400 nm), is photocarcinogenic as well and, e.g., can cause the formation of cyclobutane pyrimidine dimers in nuclear DNA and thereby exert mutagenic and immunosuppressive effects. An increasing number of studies conducted during the last 15 years, however, suggest that this is not the end of the story but that in fact, wavelengths in natural sunlight beyond the UV spectrum can damage human skin as well. Such studies have mainly focused on two types of nonionizing radiation: (1) the blue light part of visible light (400–495 nm) as well as (2) near-infrared radiation, i.e., IRA (770–1400 nm).
J. Krutmann (*) • K. Sondenheimer S. Grether-Beck • T. Haarmann-Stemmann IUF—Leibniz Research Institute for Environmental Medicine, Düsseldorf, Germany e-mail: [email protected] © Springer International Publishing Switzerland 2018 J. Krutmann, H.F. Merk (eds.), Environment and Skin, https://doi.org/10.1007/978-3-319-43102-4_2
The existing evidence that such radiation types can damage human skin has recently been summarized in a number of state-of-the-art reviews [1, 2]. In this chapter, rather than simply repeating this knowledge, we will provide a brief summary of the major findings coming from such studies and, for more detailed information, refer the interested reader to the respective publications. Instead, we will put forward and discuss the hypothesis that most of our current knowledge as it concerns sunlight-induced health damage to human skin might be biased by the irradiation protocols that were used. Accordingly, in the vast majority of studies, skin responses have been studied which were elicited by either UVB alone or UVA alone or blue light alone or IRA alone. This is in marked contrast to real exposure scenarios, where human skin is exposed to all these wavelengths simultaneously, because they are all present in natural sunlight. We will discuss the existing evidence that signaling responses elicited in skin cells by different wavelengths might interact with and thereby influence each other and that the resulting responses are different from the ones induced by each of the single irradiations. We will also put forward the hypothesis that it is mandatory to study the combined rather than additive effects of different wavelengths within and beyond natural sunlight 11
J. Krutmann et al.
12 Exposure to single spectrum UVA VIS
UVB
REA
L
P
IRA
ICT
TURE
Sequential exposure to 2 or more spectra UVB > IRA UVB > UV
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