Final answer:
A moderator that aggravates an individual's response to a stressor is the individual's subjective appraisal of the situation; the more threatening the event is perceived, the greater the stress response. History of trauma and chronic stress also serve as moderators that can exacerbate stress reactions.
Step-by-step explanation:
A moderator that can aggravate an individual's response to a stressor typically involves the individual's perception and appraisal of a situation. If a person views an event as particularly harmful or threatening, and believes that they lack the resources to cope, this appraisal can intensify their stress response. Cognitive appraisal is a key moderator in how stress is experienced. Stemming from the seminal work of Selye (1976), stress is highly subjective – 'it's not so much what happens to you as it is how you respond.' Thus, the manner in which an individual appraises a stressor – as harmful or manageable – plays a pivotal role in determining the level of stress they experience.
An example of a moderator that could aggravate stress responses is an individual's history of trauma, which can wire stress reactivity in a way that responses to future stressors become more pronounced. Chronic stress can also serve as a moderator by weakening the immune system and making individuals more susceptible to health problems, thereby aggravating the stress response to new stressors.