There are two types of ultraviolet photons contained within natural sunlight, and it is these photons that damage DNA by producing free radicals. In the short term the damage is sunburn, however in the long-term it causes premature ageing and many new cases of skin cancer every year.
The UV rays that we are exposed to consist of UVA and UVB photons. UVB rays are shorter in wavelength and do not penetrate deeply into the skin. They cause significant damage to the DNA resulting in sunburn and cancer. It is UVA rays that have a longer wavelength, thus they penetrate deep into the layers of skin and cause skin ageing as well as immunologic problems.
It is the role of sunscreen to protect against these UV rays. It does this by acting like a very thin bulletproof vest, stopping the rays before they reach the skin and cause the damage. It contains organic sunscreen molecules that absorb UV and inorganic pigments that absorb, scatter and reflect UV.
Click here for how
ultraviolet light kills cells.