Directions for use given by manufacturers of consumer products are often based on ideal conditions of use. However, each user is different and has complex user characteristics which may impact the directions of manufacturers and thus divert a product's primary functions. In this study we therefore propose examining this phenomenon of use in eco-designed laundry detergents. Initially designed to respect the environment, are they always environmentally-friendly in real conditions of use and what factors can reverse their benefits? After a state of the art in eco-designed laundry detergents and major criteria for use, we present the statistical analyses and tests which show the importance of knowing and modelling real uses so as to better design and adapt such products.