Until now, a product’s SPF (sun protection factor) was the only objective measure of its ability to protect against sunburn. SPF does not, however, provide any measure of protection against developing skin cancer, or of premature aging caused by the sun’s rays known as photoaging. Sun damage is caused by two types of radiation: ultraviolet A (UVA) and ultraviolet B (UVB). UVB is important in causing sunburn. SPF is therefore a measure of how well a sunscreen product protects against UVB and sunburn.