An accessory cap for a respiratory cartridge includes a housing having a front wall and a side wall which cooperate to define an interior cavity. The side wall includes a retaining formation configured and arranged to releasably engage and hold the housing on the respiratory cartridge. The housing includes a downwardly facing air passage configured to allow air to pass from an exterior environment to the interior cavity. The accessory cap further includes a pre-filter support web removably received within the interior cavity and spaced inwardly from the front wall. The housing and the pre-filter support web form a pre-filter cavity within the interior cavity adjacent to the front wall. The accessory cap can function as a standalone shower cap, or a pre-filter media can be optionally inserted into the pre-filter cavity so that the accessory cap functions as a combination pre-filter and a shower cap.