Two main types of UV radiation concern us vis a vis our health:
1. UV-B This is the form of ultraviolet radiation that is mainly responsible for sunburning, delayed tanning and skin cancers, and it also contributes to skin ageing. It is the form used by the body to make vitamin D. It cannot penetrate beyond the superficial skin layers and is blocked by glass.
2. UV-A The relatively long-wavelength UVA accounts for approximately 95% of the UV radiation reaching the Earth's surface. It can penetrate into the deeper layers of the skin but has less energy than UVB. It is responsible for the immediate tanning effect and also contributes to skin ageing and wrinkling. For a long time it was thought that UVA could not cause any lasting damage. Recent studies strongly suggest that it may also enhance the development of skin cancers. It can pass through glass.