A trigger is any stimulus — a word, a tone of voice, a facial expression, a smell, a quality of silence, a particular combination of circumstances — that activates a stored emotional and physiological state from the past. The trigger does not cause the emotional response directly. It acts as a key that unlocks a stored memory state — and suddenly the person is flooded not just with an emotion but with the full embodied experience of a past moment: the fear, the shame, the helplessness, the rage, the grief.
The crucial distinction: a trigger is not the same as something being upsetting or painful. A painful situation in the present — genuine conflict, genuine loss, genuine disappointment — produces an appropriate emotional response that is proportional to what is actually happening, that passes as the situation resolves, and that can be processed through normal grief and communication. A triggered response has a different quality: it feels much bigger than the situation warrants, it has a compulsive quality that seems to have its own momentum, and it often includes a sense of being transported — of suddenly being younger, smaller, more helpless than the actual adult in the situation.
The test: if your emotional response to a situation seems disproportionate to what is actually happening — to you or to observers — there is likely a wound being activated beneath the surface reaction. The present person or situation has become the representative of something older and more powerful.