Visible violet and blue light can cause effects on the skin – 05/29/2023 – Equilibrium and Health

A study conducted at the University of São Paulo (USP) reveals that visible light in the violet and blue ranges can have a toxic effect on skin cells depending on the exposure time. Among the possible consequences are the release of oxidizing compounds, damage to DNA, damage to mitochondria and other organelles, and accumulation of the pigment lipofuscin, which increases cellular sensitivity to light.

Therefore, according to the authors, commercially available sunscreens, which protect against ultraviolet radiation (UVB and UVA), are not sufficient for effective skin protection.

The results of the research, carried out with the support of Fspesp (Foundation for Research Support of the State of São Paulo) during Paulo Newton Tonolli’s postdoctoral studies, were published in the Journal of Photochemistry & Photobiology, B: Biology.

The investigation was carried out within the scope of the Center for Research in Redox Processes in Biomedicine (Redoxoma), under the coordination of Professor Maurício Baptista, from the Institute of Chemistry (IQ-USP). Redoxoma is a Research, Innovation and Dissemination Center (Cepid) funded by FAPESP.

This is the first time that the effects of different ranges of visible light have been compared in relation to phototoxicity in keratinocytes – the skin cells responsible for producing keratin.

“Our article shows that the high energy blue, which we call violet here, should be one of the important targets for the development of sunscreens. Violet is very close to 400 nanometers, which is the line that separates UVA from visible light. line does not have a specific reason for the skin. It has a reason for our eyes, because we have receptors that ‘see’ violet and blue, but do not ‘see’ UVA. However, in terms of wavelength and biological effect, these radiation bands are very similar to each other”, says Baptista.

Unfortunately, according to researchers, most people, including health professionals, remain unaware of the effects of visible light on the skin, and most companies that produce sunscreens ignore the fact that visible light penetrates deeper into the skin and induces redox imbalances (between oxidant and antioxidant substances) and other cellular responses similar to those induced by UVA.

Sunbathing is healthy, excess is harmful, warns Baptista, who is also studying the benefits of light for human health. Visible light exerts positive effects, such as tissue regeneration and pain relief, and even ultraviolet radiation has beneficial roles, such as, for example, in the synthesis of vitamin D. Everything is a matter of dose.

The problem is that people feel protected by sunscreen and abuse their time under the sun. With the filter, they can be protected against ultraviolet radiation, but not against visible light. An indicator that something is not right is that, despite efforts for early detection and prevention of skin cancer, the prevalence of this cancer has been systematically increasing in the world.

toxic effects

Visible light comprises much of the energy of sunlight that reaches the earth’s surface, covering the wavelength range from 400 to 750 nanometers. To investigate the differences between these visible light ranges, the researchers irradiated immortalized human skin keratinocytes (HaCaT) with physiologically relevant doses of the four main regions of visible light: violet, blue, green, and red.

They saw that the violet/blue component of visible light behaves similarly to UVA radiation in keratinocytes, producing DNA damage. In addition, violet/blue in the analyzed doses causes the malfunction of mitochondria and lysosomes, two key organelles for maintaining cell viability, inhibiting the autophagic flow and causing the accumulation of lipofuscin – an aggregate of biomolecules and oxidized membranes resulting from the incomplete digestion by lysosomes damaged by exposure to violet/blue, which increases the sensitivity of cells to visible light.

In all experiments, violet light was more toxic than blue light, which, in turn, is more toxic than green light. Only red light, at the dose used, did not cause significant damage to the studied biological targets. “This happens because there are more endogenous photosensitizers that absorb in violet than in blue and green, and almost none in red. These photosensitizers are the key to all of this”, explains Baptista.

Human skin is constantly hit by light. There are billions of photons that penetrate the different layers of the skin, influencing its physiology. The damage mechanisms induced by solar radiation are mainly due to photosensitization, a process in which photosensitizers transform light energy into chemical reactivity. Photosensitizers are molecules that absorb photon energy and pass from the ground state to the excited state, which is more reactive.

UVB rays are the most harmful for humans, because they are absorbed by DNA and the photochemical effect is more direct. “DNA itself is the photosensitizer of UVB radiation”, says the professor from IQ-USP.

In the case of visible light, photosensitization is indirect and depends on the various endogenous photosensitizers present in human skin, which absorb radiation and generate reactive oxidants. Photosensitizers are primarily vitamins, coenzymes and other cofactors, including flavin, folic acid, nicotinamide, porphyrins and their derivatives, and endogenous pigments such as melanin and lipofuscin.

The susceptibility of cells, tissues and organelles to damage caused by solar radiation depends on the presence and concentration of these endogenous photosensitizers. “Mitochondria and lysosomes, for example, have a large amount of flavoproteins and, therefore, of flavins”, states the researcher.