UVB (wavelength ~290-320nm) is responsible for around 5% of the UV radiation reaching Earth, with the majority of it also being absorbed by the atmosphere. It causes your skin to produce more melanin, which is what causes the tanning effect of sitting in the sun. However, it can also cause sunburn, and direct DNA damage, which can increase the risk of developing skin cancer. Sunscreen has been available as a product since around 1928, and most early sunscreens were formulated to screen the skin against UVB rays.