Dictionary Definition:
Noun
a: a piece (such as a lever) connected with a catch or detent as a means of releasing itespecially : the part of the action moved by the finger to fire a gunb: a similar movable part by which a mechanism is actuatedtrigger of a spray gun2: something that acts like a mechanical trigger in initiating a process or reaction~ Merriam-Webster
Elizabeth's take on this term...
The exposure to something outside the human body may trigger the inflammatory response, resulting in undesirable symptoms in the body.
An inflammatory trigger may be a food or drink, a chemical additive or preservative, a fragrance or added flavor chemical, a pharmaceutical, an air- or water-borne contaminant, a parasite, or anything else foreign to the natural integrity of the human body. Exposure to a trigger may cause symptoms of pain, discomfort, or dysfunction.