The invention concerns a device 51 for mixing at least two components, characterised by the fact that the mixing device 51 comprises two containers 52 and 53 each provided with: a. at least one opening 110 connected by a conduit 55 and provided with a device allowing the available volume of the containers 52 and 53 to be varied alternately, pistons 50 that are able to be moved in opposing directions, so as to transfer the content from one of the containers 52 or 53 into the other container 52 or 53 through the openings 110 and the conduit 55; and b. at least one inlet opening X allowing the at least two components to enter; said mixing device not comprising an additional outlet opening, one of the inlet openings X allowing both at least one component to enter, and the mixture of the at least two components obtained to leave. The invention also concerns a method for mixing cosmetic components using this mixing device and a device for manufacturing and dispensing a customised cosmetic composition comprising said mixing device.