A dispenser device, including an outlet, air expeller including a piston that slides in an air chamber between rest position and dispensing positions, and a reservoir containing a dose composition. The reservoir includes an air inlet connected to the air expeller, and a composition outlet connected to the outlet, the air inlet including a composition retainer member, and the composition outlet being closed by a closure element force fitted in the composition outlet of the reservoir. A mechanical opening system co-operates with the closure element to expel it from its closed position while the device is actuated. The piston, when in its rest position, co-operates in non-airtight manner with the air chamber so that the air chamber communicates with the atmosphere. The piston includes an inner lip co-operating with a cylindrical surface, the cylindrical surface including fluting co-operating in non-airtight manner with the inner lip in the rest position.