Dermatologists frequently denounce the danger of long UVA rays and infrared rays.

Marketing arguments or real threat to our skin? We surveyed the best specialists.

UVA, UVB, UVC and infrared: different wavelengths

There are three types of UV radiation:

UVAs: from 315 to 400 nanometers (nm), more numerous and more penetrating than UVB, they are the cause of photoaging. They excite the DNA, which can be a source of mutations and even cancers . The long UVAs range from 370 to 400 nm.

UVB: from 280 to 315 nanometers, they stay in the superficial layers of the skin. They are responsible for tanning, burns, inflammation, promote aging of the skin and skin cancers.

UVC: from 153 to 280 nanometers. These are the most harmful, but they are filtered by the ozone layer and do not reach us.

Infrared: they are invisible to the naked eye. Their wavelength, much larger than that of UVA and UVB (between 780 nm and 1 000 000 nm), allows them to reach the deepest layers of the skin. They produce the sensation of heat due to the sun .

How to protect yourself from UVA and UVB?

UVA / UVB, the finding: "A few years ago, it was thought that only UVB were harmful," says Nathalie Broussard, director of communication science Vichy. They cause burns, promote the aging of the skin and the appearance of skin cancers. "But we realized that UVAs are much more numerous (95% of UV radiation versus 5% for UVB) and that 75% of long UVA is very dangerous. These do not depend on the seasons, pass through the closed windows and penetrate the deep layers of the skin   She says.

There they wreak havoc: they touch nearly a thousand genes in the dermis and the epidermis, degrade collagen and elastin, produce a large number of free radicals, reach the DNA and thus favor the appearance of skin cancers.

In the face of UVA the solution: to develop a combination of filters able to prevent the long UVA to penetrate the epidermis and the dermis. The legislation imposes a ratio of one to three between anti-UVB and anti-UVA (an SPF30 must be accompanied by an anti-UVA of 10). Solar products now contain much stronger anti-UVA filters, which sometimes go up to 50 protection, equal to SPF.

In the opinion of specialists, it is necessary to choose not the accumulation of filters but the right combination for organic and mineral filters to act synergistically. A great way to limit the number.

To fight against the UVA and UVB, the flat: one wonders if filters too numerous, too powerful are not likely to be harmful and to cause intolerances or allergies .

Infrared: weapons to defend your skin

The infrared, the report: "Several studies prove the deleterious infrared [IR], says Olivier Doucet, vice president research and development of Lancaster laboratories. Their wavelength allows them to strike deeply and alter to the deepest layers of the skin. IRs produce a large amount of free radicals that can cause DNA damage, accelerated photoaging, and altered cell function. "

In the face of infrared, the solution: there is no molecule capable of absorbing IR radiation. "At Lancaster, we've combined reflectors with antioxidants to neutralize the action of IR. Their radiation is significantly attenuated. "

Therefore formulas that reflect infrared, preventing them from penetrating the skin, and that contain a high concentration of antioxidants to put the free radicals out of harm's way.

Fight infrared, flat: "Infrared is useful as a warning signal, says Lionel Benetti (Clarins). I had developed sunscreens with IR protection, but serious and recent studies by Professor Dubertret tend to show that IR-induced aggression could be beneficial in preparing the skin to fight oxidative stress. and improve its adaptation to the sun. "