UVA radiation

UVA radiation is a type of ultraviolet (UV) radiation with wavelengths between 320 and 400 nanometers (nm). UV radiation is part of the electromagnetic spectrum, undetectable by the human eye, and lies between visible light and X-rays.12

UV radiation is categorized into four regions: near (400–300 nm), middle (300–200 nm), far (200–100 nm), and extreme (below 100 nm). Biologically, it's divided into UVA (400–315 nm), UVB (315–280 nm), and UVC (280–100 nm).2

While most UV radiation from the sun is absorbed by Earth's ozone layer, nearly 99% of the UV that reaches the surface is UVA. UVA radiation is known to cause tanning and contribute to skin aging. UVB radiation is responsible for many of UV's effects on organisms, and UVC is more hazardous but largely absorbed by the atmosphere.213