trigger

Definition of trigger

trigger

(TRIH-ger)
In medicine, a specific event that starts a process or that causes a particular outcome. For example, chemotherapy, painful treatments, or the smells, sounds, and sights that go with them may trigger anxiety and fear in a patient who has cancer. In allergies, exposure to mold, pollen or dust may trigger sneezing, watery eyes, and coughing.

Source: NCI Dictionary of Cancer Terms