A day out in the sun is a health panacea. It lifts our mood (by increasing serotonin levels, just like antidepressant drugs) and boosts vitamin D synthesis, which is the key to healthy bones and to prevent osteoporosis, plus a lot more! (1) However, UV light promotes ageing and increases the risk of getting skin cancer, thus using sunscreens is essential. Recent evidences, though, suggest that it is not only UV light that can harm our skin.
Sunlight exposure triggers the secretion of a mood-lifting and calming hormone called serotonin. (1b) Photo by Zwaddi on Unsplash
Sunlight is electromagnetic waves emitted by the sun with different wavelengths: some waves are visible to the human eyes, while UV and infrared waves are not. Visible light is not homogenous but is composed of continuous wavelengths corresponding to the entire range of colors in the rainbow. UV radiation is well-known for its damaging impact and carcinogenesis but it occupied less than 5% of solar energy. (2) Meanwhile, almost 50% of sunlight’s energy (2) is in the visible range, amplifying whatever impact visible light poses on the skin. Moreover, visible radiation also has the ability to penetrate more deeply in the skin compared to UV light.
A recent study has now suggested that visible radiation may in some circumstances cause damage to our skin. However, not the whole visible radiation is similarly harmful. It is the blue light, the region closer to the UV band, that bears the highest risk of premature skin ageing, whereas no apparent risks are given by red light, at the other end of the spectrum. Blue light, interestingly, increases melanin production and skin pigmentation; (3) and it has a synergic effect with UV light. (4) In contrast, red light exerts no impact on pigmentation. (3) Is this finding possibly of relevance to us? It might, as the light dosage used in the study is equivalent to roughly 2.5 hours under the sun. Although it takes only 20 minutes to induce similar pigmentation with UVB, the data is worth concerning. (3) Research also shows that blue light decreases cell viability (5) while red light does not and instead, it speeds up wound healing. (6)
Blue light, similarly to UV light, is now suggested to increase free radicals in cells. Free radicals are highly active molecules and play an important role in defense mechanism against pathogens but when they are excessive (this situation is called oxidative stress), they will interact with biomolecules and harm cells. (7) Under oxidative stress, a program that is known as senescence, or skin ageing, is activated, leading to the degradation of elastin and collagen.(8) The more UV and blue light, the more damage to skin cells. (5) There are also evidences that blue light has other effects, including altering the skin’s circadian rhythm, which results in changes in skin repair processes at night (9), and inducing skin dehydration (by decreasing the number of water channels on skin cells). (10)
Time lapse photo of blue light. Photo by Madeleine Ragsdale on Unsplash
So, is the fact that visible light causes damage a major worry? Probably not. Data so far has not yet proved blue light or visible radiation to be carcinogenic like UVB. Nonetheless, in order to maintain skin’s youthfulness and prevent premature skin ageing, it is better not to stay under the sun for too long even with sunscreen on since normal sunscreens are not able to protect us from visible light.
What's about the blue light emitted from screens of electronic devices, for example your iPhone? Blue light from these sources is roughly 60 times less strong compared to sunlight and only an accumulation of around 2000 hours affect skin fibroblasts. (11) Thus, it is advisable to reduce your time in front of the screen to avoid additional accumulated ageing induction, but if you only consider screen-emitted blue light (the screens do emit other types of radiation), it is far less influential than its component in sunlight.
Reference 1. (a) What Are the Benefits of Sunlight? https://www.healthline.com/health/depression/benefits-sunlight (accessed 4/12/2019); (b) van der Rhee, H. J.; de Vries, E.; Coebergh, J. W., Regular sun exposure benefits health. Medical Hypotheses 2016, 97, 34-37. 2. Sunlight. https://en.wikipedia.org/wiki/Sunlight (accessed 19/11/2019). 3. Duteil, L.; Cardot-Leccia, N.; Queille-Roussel, C.; Maubert, Y.; Harmelin, Y.; Boukari, F.; Ambrosetti, D.; Lacour, J.-P.; Passeron, T., Differences in visible light-induced pigmentation according to wavelengths: a clinical and histological study in comparison with UVB exposure. Pigment Cell & Melanoma Research 2014, 27 (5), 822-826. 4. Kohli, I.; Chaowattanapanit, S.; Mohammad, T. F.; Nicholson, C. L.; Fatima, S.; Jacobsen, G.; Kollias, N.; Lim, H. W.; Hamzavi, I. H., Synergistic effects of long-wavelength ultraviolet A1 and visible light on pigmentation and erythema. British Journal of Dermatology 2018, 178 (5), 1173-1180. 5. Lawrence, K. P.; Douki, T.; Sarkany, R. P. E.; Acker, S.; Herzog, B.; Young, A. R., The UV/Visible Radiation Boundary Region (385–405 nm) Damages Skin Cells and Induces “dark” Cyclobutane Pyrimidine Dimers in Human Skin in vivo. Scientific Reports 2018, 8 (1), 12722. 6. Li, Y.; Zhang, J.; Xu, Y.; Han, Y.; Jiang, B.; Huang, L.; Zhu, H.; Xu, Y.; Yang, W.; Qin, C., The Histopathological Investigation of Red and Blue Light Emitting Diode on Treating Skin Wounds in Japanese Big-Ear White Rabbit. PLOS ONE 2016, 11 (6), e0157898. 7. Juránek, I.; Nikitovic, D.; Kouretas, D.; Hayes, A. W.; Tsatsakis, A. M., Biological importance of reactive oxygen species in relation to difficulties of treating pathologies involving oxidative stress by exogenous antioxidants. Food and Chemical Toxicology 2013, 61, 240-247. 8. Rinnerthaler, M.; Bischof, J.; Streubel, M. K.; Trost, A.; Richter, K., Oxidative Stress in Aging Human Skin. Biomolecules 2015, 5 (2), 545-589. 9. Dong, K.; Goyarts, E. C.; Pelle, E.; Trivero, J.; Pernodet, N., Blue Light disrupts the circadian rhythm and create damage in skin cells. International Journal of Cosmetic Science n/a (n/a). 10. Avola, R.; Graziano, A. C. E.; Pannuzzo, G.; Cardile, V., Blue Light Induces Down-Regulation of Aquaporin 1, 3, and 9 in Human Keratinocytes. Cells 2018, 7 (11), 197. 11. Rascalou, A.; Lamartine, J.; Poydenot, P.; Demarne, F.; Bechetoille, N., Mitochondrial damage and cytoskeleton reorganization in human dermal fibroblasts exposed to artificial visible light similar to screen-emitted light. Journal of Dermatological Science 2018, 91 (2), 195-205.