Background. Recent neurobiological models provide a possible mechanism of daily life stress directly affecting the intensity of psychotic experiences in vulnerable individuals. In order to validate such a mechanism, the impact of daily life stress on psychosis intensity was investigated in two groups at increased risk of onset (relatives) and relapse (patients) of psychosis.

Method. Patients with psychosis in a clinical state of remission (n=42), first-degree relatives (n=47), and control subjects (n=49) were studied with the Experiencing Sampling Method (ESM is a structured diary technique assessing current context and psychopathology in daily life) to assess (1) appraised subjective stress related to daily activities and events, and (2) intensity of subtle psychotic experiences in daily life.

Results. Multilevel regression analyses revealed significant increases in psychosis intensity associated with increases in subjective activity – and event-related stress in patients. First-degree relatives reported increases in psychosis intensity in relation to activity-related stress but not event-related stress. No association was found in control subjects.

Conclusions. Subjects at increased risk for psychosis show continuous variation in the intensity of subtle psychotic experiences associated with minor stresses in the flow of daily life. Behavioural sensitization to environmental stress may therefore be a vulnerability marker for schizophrenia, reflecting dopaminergic hyper-responsivity in response to environmental stimuli.