"The Sun Protection Factor is the ratio of the minimum erythemal dose on skin protected by a sunscreen product to the minimum erythemal dose on the same unprotected skin."* SPF is the abbreviation of "Sun Protection Factor". The SPF measurement is based on the erythematous response of the skin due to UVB, i.e. how long it takes for protected skin versus unprotected skin to burn. The calculation of the SPF indicates theoretically how long you can stay in the sun without burning, depending on the protection you have applied. The higher the index, the more the skin is protected. *according to the European Commission recommendation of