In vitro UVA:UVB Boots Star Rating system (revised in 2011)

The UVA measurement method used to allocate UVA:UVB ratio protection categories in accordance to the Boots Star Rating system (2011 revision) is based upon an in vitro spectrophotometric measurement technique in which the tested product is spread using adequate substrate and exposed to a representative dose of sun-simulated ultraviolet radiation, to allow for any photo-instability of the active ingredients contained within the sun protection product.