2. Sun protection products

2.1 Reminders about the solar spectrum

The solar spectrum extends from cosmic rays to radio waves, including UV radiation at wavelengths between 200 and 400 nm. Although UV radiation accounts for only 5% of the radiation reaching the earth's surface, it is responsible for the vast majority of observed biological effects on the skin. In 1932, William Coblentz proposed the division of the UV spectrum into 3 zones: UVC (200 – 290 nm), UVB (290 – 320) and UVA (320 – 400 nm). The UVA range is itself subdivided into 2 zones: short UVA or UVA1 (320 – 340 nm) and long UVA or UVA2 (340 – 400 nm). UV radiation reaching the earth's surface is 95% UVA and 5% UVB. Although in the minority, it is UVB that is responsible for the greatest number of skin symptoms, due to its energy, which is inversely...