nano materiaLs Provide Broad-spectrum Sun Protection
UltravioLet Radiation and the Skin
Ultraviolet radiation (UVR) from sunlight is only about 5% of the total amount of electromagnetic radiation reaching the Earth's surface; however, it has been shown to be very harmful to the skin. Electromagnetic radiation is classified according to wavelength (1nm =10-9 m), and shorter wavelengths have higher frequencies and higher energy.
The dimensions of the relevant UV wavelengths begin at 290 nm and extend;through 400 nm (Figure 2) and are classified as UVE (290-320 nm) and UVA (320-400 nm).
Most of the UV radiation reaching the earth is surface is UVA.Radiation between 400 -700 nm is classfiend as visible (light), and above 700 nm is infrared heat). Radiation below 290 nm is UVC and is highIy damaging.However UVC is screened out by the ozone layer of the atmosphere and does not reach the earth's surface.
Excess exposure to both UVA and UVB radiation are known to be risk factors for skin cancer as well,so the need for broad-spectrum filters for skin protection clearly has been established. Titanium dioxide (TiO) and zinc oxide (ZnO) long have been recognized as efficient particulate agents that filter UVA and UVB from solar radiation