Until very recently, the talk about sun protection was focused on ultraviolet (UVs): UVB [280-315 nm] then UVA [315-380 nm].
Indeed, these high energy radiations that lead to the appearance of tanning also cause the appearance of erythema, free radicals and premature ageing.
However, UVs represent only 7% of radiation reaching the earth's surface; the remainder consists of visible light (46%) and infrared (IR) (47%) (Figure 1).
Figure 1: Spectrum of solar radiation reaching the Earth
In the 1990s, the first claims concerning cutaneous protection against IR appeared  but it was not until the end of the 2000s that this argument was more widely used by brands.
At the same time, attention has been focused on the impact of visible light on our skin, and more particularly the blue light that invades our environment via screens, tablets, smartphones and other electronic devices.
Figure 2: Average spectrum of visible radiation emitted by screens
The IR spectrum extends from 780 to 106 nm and decomposes to IRA [780-1480 nm], IRB [1480-3000 nm] and IRC [3-1000 μm] (Figure 3).
Figure 3: Splitting of the infrared spectrum
While sunscreens protect against UV radiation, several studies point out the deleterious impact of IR and the fact that IR protection should also be added to products [2-4].
Indeed, IR are involved in skin ageing and probably in carcinogenesis ; they are mainly responsible for the increase of skin temperature and lead to the production of free radicals and metalloproteinases-1 (MMP-1) in the dermis [6-8].
Effective protection against IR can be achieved by adding absorbing optical filters in the IR range, free radical scavengers and / or photon reflection .
Dermscan proposes to evaluate the protective effect of cosmetics against infrared by complementary approaches, after IR irradiation :
- biometric approach: cutaneous measures of color and/or temperature and/or microcirculation
- biochemical approach: lipid oxidation assays (SQOOH, MDA) and/or enzymes (CAT, SOD)
The spectrum of blue light extends from 380 to 490 nm, passing from violet to indigo then to blue (Figure 4).
Figure 4: Splitting of visible light
Recent studies have shown that this type of light - especially short wavelengths around 415 nm - could lead to erythema, free radical production and long-lasting hyperpigmentation in phototype subjects III and more [11,12].
Current chemical filters are not able to block visible light, and blue light in particular. Only mineral filters can - depending on the size of the particles - filter blue radiation .
Another approach is to add anti-oxidants to the cosmetic formulas to limit accelerated skin ageing and damage caused by blue light .
Dermscan offers different approaches to evaluate the anti-blue light protective effect at the level of the skin:
- Irradiation (single or repeated) in blue light (peak at 415 nm) followed by evaluation of β-carotene oxidation, protein carbonylation, lipid oxidation or pigmentation.
- Test in real conditions, on subjects regularly exposed to the screens of electronic devices: effect on the radiance of the complexion and the cutaneous fatigue.
To find out more about test protocol contact Dermscan at firstname.lastname@example.org
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