Phototoxicity is defined as a toxic response that is elicited after exposure of the skin to certain chemicals and subsequent exposure to light. The approved 3T3 NRU phototoxicity test is based on submersed BALB/c 3T3 fibroblasts. Hence it is limited to soluble chemicals. As the use of EST1000 enables to apply compounds topically these models are more physiological and therefore more reliable and are used as a second tier approach.