A nebulizer head, comprising: - a housing structure providing a bidirectional air-flow path between two opposite air-flow openings (18a, 18b), wherein one of the air-flow openings is provided as a mouth-piece opening and another one of the air-flow openings is provided as a backside opening, and wherein a flow direction from the backside opening to the mouth-piece opening is a first air-flow direction for inhaling and a vice versa flow direction is a second air-flow direction for exhaling; - a fluid reservoir provided to accommodate a liquid from which small droplets are to be generated in order to form an aerosol; - an aerosol generator with an aperture member that comprises an aperture surface with a plurality of apertures to provide the small droplets from the liquid; wherein the fluid reservoir is arranged adjacent the aerosol generator such that the aperture member is in contact with the fluid, wherein the aperture member is mounted substantially vertically in the nebulizer head in relation to the air-flow path which is, in normal use of the nebulizer head, arranged horizontally; wherein the aerosol generator is arranged within the air-flow path; wherein at least one by-pass flow path is provided between the aerosol generator and the housing structure, wherein the by-pass flow path is arranged around the aerosol generator, and wherein a flow direction of the by-pass flow path is the same as the second air-flow direction; wherein the air enters the air-flow path and leaves the air-flow path via the air-flow openings; wherein the aperture surface is arranged transverse to the first and second air-flow direction; and wherein the air-flow is manually activatable by the user breathing in and out respectively; and wherein the air-flow is non-supported by ventilation means. - a housing structure providing a bidirectional air-flow path between two opposite air-flow openings (18a, 18b), wherein one of the air-flow openings is provided as a mouth-piece opening and another one of the air-flow openings is provided as a backside opening, and wherein a flow direction from the backside opening to the mouth-piece opening is a first air-flow direction for inhaling and a vice versa flow direction is a second air-flow direction for exhaling; - a fluid reservoir provided to accommodate a liquid from which small droplets are to be generated in order to form an aerosol; - an aerosol generator with an aperture member that comprises an aperture surface with a plurality of apertures to provide the small droplets from the liquid; wherein the fluid reservoir is arranged adjacent the aerosol generator such that the aperture member is in contact with the fluid, wherein the aperture member is mounted substantially vertically in the nebulizer head in relation to the air-flow path which is, in normal use of the nebulizer head, arranged horizontally; wherein the aerosol generator is arranged within the air-flow path; wherein at least one by-pass flow path is provided between the aerosol generator and the housing structure, wherein the by-pass flow path is arranged around the aerosol generator, and wherein a flow direction of the by-pass flow path is the same as the second air-flow direction; wherein the air enters the air-flow path and leaves the air-flow path via the air-flow openings; wherein the aperture surface is arranged transverse to the first and second air-flow direction; and wherein the air-flow is manually activatable by the user breathing in and out respectively; and wherein the air-flow is non-supported by ventilation means.