Today’s sunscreens must prove, more than ever, their efficiency and safety since, among all other products, they are the object of crucial health-related regulations. Sunscreen product companies must therefore give consumers a reliable sun protection factor (SPF). To determine SPF, an in vivo test should be used (per ISO 24444)—i.e., creams tested on the backs of volunteers.1 However, such tests present several inconveniences, including cost and ethical concerns. For all these reasons, companies and the European Commission turned toward the development of in vitro methods.
