Highlights from

EADV 2019

28th EADV Congress

Madrid, Spain 9 - 13 October 2019

The underestimated effect of visible light

Until recently, visible light (400-700 nm) has been regarded to have no significant cutaneous photobiologic effects [1]. However, they contribute to the ROS production and to skin damage attributed to UV light.

“We should not forget that not only UV light but also visible light contributes to the production of ROS,” said Dr Serena Lembo (University of Naples Federico II, Italy). Irradiation of human skin equivalents with visible light has been shown to induce production of ROS, proinflammatory cytokines, and matrix metalloproteinases (MMP)-1 expression in a dose dependent manner [2]. Another trial assessed the free radical induction by sunlight in different spectral regions [3]. It showed that although UV light stimulated the most intensive radical formation, visible light and even near infrared light also considerably contributed to the free radical formation. Half of all free radicals generated in the whole solar spectrum are induced by visible light and near infrared light [3]. According to this trial, visible light energy is not potent enough to produce radicals directly. However, within the mitochondria and by the activity of several enzymes, ROS are produced. The effect of visible light in the extracellular matrix is very similar to UV radiation: it increases MMP-1 and MMP-9 expression and decreases type 1 procollagen levels in human skin in vivo, thus contributing to photoaging [5].

Visible light penetrates deep into the dermis. The erythema is considered a result of dilatation of the vasculature of the subpapillary plexus. Production of radicals also induces inflammatory processes and this chronic process might contribute to DNA damage and carcinogenesis. Although sunscreens effectively protect against UV radiation, they are not as efficient stopping visible light and infrared light. Thus, the levels of skin ROS may still overcome the natural antioxidant reservoir in the skin and cause skin damage [2,4].

Dr Lembo also mentioned a study that showed that immediate pigment darkening induced by visible light is not significantly different from that produced by UV [6]. “In this study, visible light even induced a more potent and more long-lasting pigmentation compared with UVA1,” said Dr Lembo. Compared with UVB irradiation, the shorter wavelengths of visible light, the blue-violet light, induced a significantly more pronounced hyperpigmentation that lasted up to 3 months, but only in melano-competent individuals [7]. These finding have potential implications due to the possible role of visible light in the pathogenesis of pigmentary disorders, such as melasma.

In another study, commercially available sunscreens were found to have minimal effects on reducing visible light-induced ROS. Results showed that MMP-1 expression following infrared radiation can be prevented by the addition of appropriate antioxidants [8]. Thus, increasing the antioxidant threshold of the skin is a method to increase the buffering ability of the skin against ROS induced by visible light. A poster presented during the EADV 2019 meeting demonstrated that addition of the antioxidant resveratrol can also be used successfully as a photostabiliser of a chemical UVA filter in sunscreen products, thus killing two birds with one stone [9].

Top image: @ iStockPhoto: ipopba

The content and interpretation of these conference highlights are the views and comments of the speakers/authors.