In the last few years, the desire to acquire a tan without sunbathing has grown. In response, many cosmetic companies have produced self-tanning preparations. However, to optimize these formulations, a suitable model to assess the colour induced on the skin remains to be developed. We have developed an in vitro method using a synthetic skin in order to study the efficacy of self-tanning formulations. The in vitro test was then used to study the influence of cosmetic ingredients upon the colour induced by erythrulose- or dihydroxyacetone-containing formulations. Finally, an in vivo study allowed us to relate the results obtained in vitro with those found on human skin. The results show that this in vitro test system is a reliable tool to predict the efficacy of self-tanning products.