A diffuser for a device for packaging and dispensing a product. The arrangement is particularly advantageous for foaming cosmetic products. The diffuser includes a collar which can be mounted on a container and a product diffusion head extending from the collar and provided with at least one output aperture. Preferably, the output aperture is oriented at an angle, relative to an axis of the collar, lying between 0° and 85°. The diffusion head is movable relative to the collar. Moreover, the diffusion head has an extension axis inclined with respect to a longitudinal axis of the collar, and has a size which is contained within the maximum cross-section of the collar and/or of the container.