Objectives: Harmful clinical consequences of sun light range from short to very long term effects such as sunburn, photoaging and skin cancers. Deciphering the biological impacts and mechanisms of the different wavelength domains helps to understand their development and design the most appropriate photoprotection.
Introduction: Although the shortest UV rays, UVB are responsible for sunburn, photocancers, ageing or pigmentary problems due to their high energy, they only represent 5% max of total UVs. In contrast, UVA rays, especially long UVAs represent the majority of total UVs and have higher penetration properties. Beyond UVs, the Visible Light (VL) radiation represents ~40 % of total sunlight. Solar VL is now proven to contribute to hyperpigmentation and pigmentary disorders. Both long UVA and VL have therefore to be considered in photoprotection strategies.
Materials / method: Long UVA
Due to the generation of a huge oxidative stress, long UVA can induce many biological and functional alterations ranging from indirect DNA lesions formation, immune function impairment, dermal alterations, metabolism disfunction, … contributing to the clinical consequences of sun exposures. Interestingly, long UVAs also induce hyperpigmentation and molecular alterations in all skin color types, even for dark skins (FSP VI). These data support a photoprotection over the whole UV spectrum up to the longest UVA which can now be achieved by the development of new long UVA UV filters.
Results: Visible light
To better understand the role of VL in hyperpigmentations additional knowledge studies were performed. First, in a precise analysis of the relative contribution of the different VL subdomains, we showed that HEV (High Energy Visible Light), Blue light and Green light represent the major contributors in VL-induced pigmentation (47, 71 and 37 % respectively). In a second study, we showed differences between different skin color types populations. Dark skins FSP VI as well as Asian subjects FSP III showed a higher pigmentary response to VL compared to European FSP III.
Conclusion: In conclusion, photoprotection has nowadays to be considered more globally, taking into account solar rays such as long UVA and VL, especially for daily photoprotection. In addition, photoprotection recommendations should also include all the skin color types, even the darkest ones.
References
Bernerd et al, Int J Mol Sci. 2022 Jul 26;23(15):8243.
Regazzetti et al, J Invest Dermatol. 2018 Jan;138(1):171-178.
Marionnet et al,. J Eur Acad Dermatol Venereol. 2023 Apr;37 Suppl 4:3-11.
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