A pump dispenser having a bottle with a neck and a pump assembly. The pump assembly includes an actuator, a closure connected to the actuator and coupled to the neck of the bottle, a dip tube, and a dual chamber pump. The dual chamber pump includes a piston assembly, a sealing cap, and a housing, which includes a pump chamber, a storage chamber having a cavity, and a core. The sealing cap is rigidly connected to the core and closes the storage chamber at a lower portion such that the substance to be released remains stored in the storage chamber cavity. When the actuator is pushed down for a first time by a user, a piston assembly moves to push down a connecting stem, which pushes down the sealing cap to open the storage chamber for releasing the substance contained in the storage chamber from the bottle.