Embodiments disclosed herein are directed to systems and methods for protecting needleless injector units from one or more contaminants. In an embodiment, a needleless injector system includes a needleless injector unit and an auxiliary unit. The needleless injector unit has a nozzle portion and a supply of one or more substances for injection. The needleless injector unit is configured to inject the one or more substances from the nozzle portion through a skin surface of a subject. The auxiliary unit is coupleable to the needleless injector unit. The auxiliary unit includes a source of one or more protectants and is configured to emit the one or more protectants in a region between the nozzle portion of the needleless injector unit and the skin surface of the subject.