Background
The stress–vulnerability model of psychosis continues to be influential. The aim of this study was to compare emotional and symptomatic responses to stress in individuals at ultra-high risk (UHR) of developing psychosis, in age- and gender-matched healthy controls, and in patients with non-affective psychosis.

Method
A total of 27 UHR, 27 psychotic and 27 healthy individuals completed the experience sampling method, an ambulant diary technique, where they were required to fill in self-assessment questions about their emotions, symptoms and perceived stress at semi-random times of the day for 6 days. Quesionnaire and interview assessments were also completed.

Results
Multilevel regression analyses showed that individuals at UHR of developing psychosis reported greater negative emotions in response to stress than the healthy individuals. Against the initial hypotheses, the UHR individuals also experienced greater emotional reactivity to stress when compared with the patient group. No significant differences were observed between the patients and the non-clinical sample. Stress measures significantly predicted the intensity of psychotic symptoms in UHR individuals and patients, but the extent of this did not significantly differ between the groups.

Conclusions
Individuals at UHR of developing psychosis may be particularly sensitive to everyday stressors. This effect may diminish after transition to psychosis is made and in periods of stability. Subtle increases in psychotic phenomena occur in response to stressful events across the continuum of psychosis.