Your skin protects you from the outside world, but it needs a bit of help to protect you from UVA and UVB rays.
Ultraviolet light (UV light) is radiation from the sun and is invisible to the human eye. UV light can penetrate deep into our skin and is responsible for sunburn, the formation of free radicals that damage our skin, and for increasing the risk of skin cancer.
Sunscreen protects your skin against damage caused by exposure to UV rays by means of UVA and UVB filters that absorb and reflect harmful UV light. When you apply sunscreen, the UV filters form a thin, protective barrier on the surface of your skin and essentially absorb the harmful UV radiation before it penetrates and damages your skin.
UVA filters protect the skin from UVA rays, which make up 95 percent of the UV light reaching the Earth's surface. UVA rays also penetrate deep into the skin are known to be instrumental in speeding up the skin aging process.
Similarly, UVB filters protect the skin from UVB light, which is the main cause of sunburn and the development of skin cancer. It only penetrates the outer layers of the skin, but is no less dangerous than UVA light.