Ultraviolet: what is it?

We qualify as ultraviolet radiation (UV), electromagnetic radiation of the same nature as visible light. However its wavelengthsbetween 20 nm and 400 nm, are too short to be perceptible by thehuman eye. L’energy that this radiation transports, on the other hand, is all the more important as the wavelength is weak. It can cause harm to the human body.

Ultraviolet can be produced by artificial sources such as lasers or tanning lamps. However, they mainly come to us from the Sun. It is 5% of the radiation that we receive at sea level — because the amount of UV radiation received increases with altitude — which is thus composed of UV, mainly UVA (98%), but also a few UVB rays (2%).

Ultraviolet rays and health

Ultraviolet radiation is divided into three main categories:

• UVA rays are found at wavelengths between 320 and 400 nm. They are the least energetic, but also the most penetrating. They are called “tanning agents” because they cause a pigmentation immediately from the skin. They also contribute to the aging of the skin and the lens and can lead to changes genetic at the beginning of skin cancers ;
• UVB rays, whose wavelength oscillates between 290 and 320 nm, are a little more energetic and partially stopped by the ozone layerand totally by the glass and the clouds . In case of overexposure, they can cause inflammatory reactions, Sun burneven burns. They also alter the genetic heritage of cells;
• UVC rays, which are between 100 and 290 nm, are very energetic and extremely dangerous for health. Fortunately, they are completely stopped by the ozone layer .

But UV radiation also has positive effects on our health. Exposing yourself to the UVB rays of the Sun for a few minutes a day makes it possible to synthesize vitamin D which facilitates theabsorption from calcium and phosphorus by the body. And UVB rays also help to treat diseases such as psoriasisor theeczema. UVC can be used by hospitals for example as sterilizing agents. They are indeed germicides. UVA rays, for their part, would help to limit the development of myopia.

The UV index makes it possible to assess the risk incurred and is accompanied by advice on how to limit it. Under an index of 1, for example, the risk is low, but wearing glasses is recommended if the day is sunny. With an index of 6, the risk is high. It is advisable to wear glasses and a hat, stay in the shade and use high protection sunscreen. When the index exceeds 11, the risk is extreme. The skin can burn in just a few minutes.