Synopsis The manufacturing of toiletries is a complex procedure and many process routes are possible for a given formulation. In the past, considerable attention has been given to the design of manufacturing equipment but there has been relatively little appreciation of the influence of physicochemical interactions during processing. These interactions are likely to be particularly important during the manufacture of dispersions such as emulsions and pastes where phase and interfacial behaviour or particle interactions can be affected by the introduction of electrolytes or surface active species. For emulsions consisting of cetyl trimethyl ammonium chloride/long chain alcohol/water, the final rheological behaviour is governed by the formation of a 'frozen' lamellar structure in the continuous phase. The phase changes occurring during processing can significantly affect the degree of structure obtained. With powder dispersions, the rheology is affected by the introduction of surface active species due to deflocculation of the particles. Even in complex product systems such as toothpastes, these changes due to powder/detergent interactions are still apparent.