Needleless injector systems, and related methods and components

A needleless injector system, comprising:

• a needleless injector unit having a nozzle portion and a supply of one or more substances for injection, the one or more substances including a fluid, the needleless injector unit configured to inject the one or more substances from the nozzle portion through a target region including a skin surface of a subject;
• an auxiliary unit coupleable to the needleless injector unit and having a source of one or more protectants, the auxiliary unit 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;
• one or more sensors configured to,
• detect one or more characteristics of at least one of one or more contaminants, the nozzle portion, the target region, or the one or more substances, wherein the one or more characteristics include at least one of presence, position, or direction of the one or more contaminants or the one or more substances;
• and
• send one or more sensing signals encoding the detected one or more characteristics;
• and
• a control unit operably coupled to the one or more sensors to receive the one or more sensing signals from the one or more sensors and configured to send an activation signal to the auxiliary unit that directs the auxiliary unit to emit the one or more protectants responsive to the one or more sensing signals.