Vulnerability Arc (Stress, Sensitization, Threshold)

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The vulnerability arc describes how repeated exposure to stress or activating events may alter our sensitivity to future stress and emotional activation over time. It helps explain why some of us experience increasing susceptibility to mood episodes or emotional dysregulation after periods of repeated activation. The arc also emphasizes interaction between environmental pressures and biological responsiveness rather than attributing outcomes to character or willpower. In this model:

• Stress is internal/external pressure that challenges emotional or biological stability (life events, interpersonal conflict, sustained high demand).
• Sensitization is how repeated stress exposure heightens reactivity, so smaller triggers produce larger emotional or physiological responses.
• Threshold is the level of stress or activation required to trigger significant symptoms In or mood changes; sensitization may lower this threshold over time.

Also see reward Hypersensitivity Model, Behavioral Approach System (BAS), Reinforcement Sensitivity