A dispenser for dispensing a fluid includes a rigid vial that has a main fluid chamber containing a fluid, and a pump assembly that is in fluid communication with the main fluid chamber and is configured to dispense a predetermined quantity of fluid from the main fluid chamber. A flexible bladder is provided which is located within the main fluid chamber and is configured to expand to fill the ullage created within the main fluid chamber during dispensing of fluid by the pump assembly. The resilient bladder tends to force itself outwardly toward the rigid vial and, in turn, increases the pressure within the main fluid chamber in comparison to the interior of the bladder to thereby prevent the ingress of air or vapors through the bladder or otherwise into the main fluid chamber.