A device for administration of an aerosol includes a generator of particles of size between 10 nm and 200 um, a mouthpiece or mouth mask for oral administration of the aerosol during the nasal exhalation phase or during the respiratory pause phase preceding nasal exhalation, and a source of gas or pressure for conveying the particles. The mouthpiece is airtight, extends beyond the teeth of the patient by a maximum length of 4 cm, and administers the aerosol for the nasal cavities, the rhinopharynx or the paranasal sinuses during aerosol administration phases, such that the is successively applied to the mouth, the rhinopharynx and then the nasal fossae and the sinuses, and then the aerosol escapes via one or both of the patient's nostrils. The device does not allow exhalation via the mouth during aerosol administration phases, and the aerosol particles not being directed to the lungs.
