Sunscreen, also known as sunblock, is a lotion, spray, gel, foam or other topical product that absorbs or reflects some of the sun’s ultraviolet (UV) radiation and thus helps protect against sunburn. Skin-lightening products may also be included in the sunscreen to help prevent melanoma and photoaging.
There are two types of UV radiation: UVA and UVB. Both cause skin damage that can lead to skin cancer. Sunscreen protects against both types of UV rays.
The effectiveness of sunscreen is measured by itssun protection factor (SPF). The SPF is a measure of how well the sunscreen protects against ultraviolet B (UVB) rays. The higher the SPF number, the greater the protection. For example, an SPF 30 sunscreen filters out 96% of incoming UVB rays; an SPF 50 blocks 98% and an SPF 100 blocks 99%. However, no sunscreen completely filters out all UV rays – even high-SPF products provide only partial protection. And remember: No matter what your sunscreen’s label says about water resistance, all sunscreens need to be reapplied after swimming or sweating to maintain their effectiveness .
When used as directed with other sun safety practices like seeking shade and wearing protective clothing, sunscreen reduces your risk of skin cancer and early skin aging caused by the sun .