Skin and sun: Ten Questions/Answers for the right protection
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Which sun protection shall one choose? Which SPF? In a sunscreen or in a moisturizing care with an SPF? Why are they so many messages about “anti-sun prevention”? What are the impacts on vitamin D? … Many questions when the topic is sun protection. The first Cosmetic Days Convention, organized by the French Cosmed, held in Marseille (France) on December 6 and 7, 2012, has allowed for the answering to many of these questions.
1. Why do I have to protect from the sun?
Sun rays comprise radiations of innumerable wavelengths. Those that are of interest here are:
• from 200 to 400 nm: UV radiation (UV);
• from 400 to 800 nm: visible radiation;
• from 800 to 1,400 nm: infrared radiation (IR).
The shorter the wavelength, the more energy the radiation transports… hence, the more aggressive it is. Thus, UV radiation is the most prone to damage our skins, in different ways, depending on their wavelength:
• from 200 to 280 nm: UVC is potentially the most harmful; however, it is blocked by the ozone layer, and does not arrive down to the ground;
• from 280 to 320 nm: UVB goes through the cutaneous barrier and the stratum corneum (the upper layer of the skin), and goes to the epidermis;
• from 320 to 400 nm: UVA goes deeper inside the skin, down to the dermis.
What are the effects on our skins?
• At the stratum corneum level, UVB and UVA dry the skin.
• At the epidermis level, UVA set off the mechanisms that allow tanning; UVB may produce sunburns. The combined action of UVA and UVB is the cause for skin cancers: basocellular and spinocellular carcinoma, the most often seen, and melanoma, less frequents but far more harmful, “concentrates of malignancy”, ...