triggering

A trauma trigger is a psychological stimulus that prompts involuntary recall of a previous traumatic experience. The stimulus itself need not be frightening or traumatic and may be only indirectly or superficially reminiscent of an earlier traumatic incident, such as a scent or a piece of clothing. Triggers can be subtle, individual, and difficult for others to predict. A trauma trigger may also be called a trauma stimulus, a trauma stressor or a trauma reminder. Read more on Wikipedia