The study involves determination of sun protection factor (SPF) values of some sunscreen formulations for their use in cosmetics. The Sun Protection Factor (SPF) is a very popular instrument in the marketing of sunscreens. Unfortunately it is often not understood how sunscreens work and where the limitations of the SPF are. A lot of aspects of the SPF are confusing, e.g. the race for higher and higher numbers, the effect on SPF when less sunscreen is applied and if sunscreen should be used at all because they may block the Vitamin D synthesis. The study explains how sunscreens work, how the SPF is determined and where the limitations of the current methods exist. The dynamic view of 'UV radiation applied' and the 'UV dose transmitted' through the sunscreen onto the skin as well as onto a substrate in vitro help in the understanding and are also promising approaches in the in vitro assessment. Sun protection factor is a laboratory measure of the effectiveness of sunscreen, the higher the SPF, the more protection a sunscreen offers against the ultraviolet radiations causing sunburn. The study is helpful in selection of sunscreens formulations used in cosmetics with better safety and high SPF values.