Sunshine contains three different bands of ultraviolet radiation: UVA, UVB and UVC. Although
UVC is the most dangerous, because it is a shorter-wavelength radiation than UVA and UVB, it is screened
out by the Earth’s ozone layer. UVA used to be thought less dangerous than UVB, but it is now known
that both bands can cause skin cancer. It is UVB which causes sunburn. However, both UVA and UVB
can age the skin prematurely.