Whenever a person become alert and ready to react they are experiencing "stress" (all so called the fight-or-flight response). A range of responses occur including physiological stress responses that prepare the body for strenuous activity. The following study measured one aspect of this physiological response, cortisol in saliva. Cortisol (shown right) is released by a part of the adrenal gland and its main function to to increase blood sugar
TITLE: Salivary cortisol response during exposure treatment in driving phobics
AUTHOR: Alpers GW et al
JOURNAL: Psychosomatic Medicine 65:679-687 (2003)
ABSTRACT: "OBJECTIVE: Extensive research on the hypothalamic-pituitary-adrenal (HPA) axis response to stress has not clarified whether that axis is activated by phobic anxiety. We addressed this issue by measuring cortisol in situational phobics during exposure treatment. METHODS: Salivary cortisol was measured in 11 driving phobics before and during three exposure sessions involving driving on crowded limited-access highways and compared with levels measured in 13 healthy controls before and during two sessions of driving on the same highways. For each subject, data collected in the same time period on a comparison nondriving day served as an individual baseline from which cortisol response scores were calculated. RESULTS: Cortisol levels of driving phobics and controls did not differ on the comparison day. Phobics also had normal cortisol response scores on awakening on the mornings of the exposures but these were already increased 1 hour before coming to the treatment sessions. Phobics had significantly greater cortisol response scores during driving exposure and during quiet sitting periods before and afterward. These greater responses generally paralleled increases in self-reported anxiety. At the first exposure session, effect sizes for differences in cortisol response scores between the two groups were large. Initial exposure to driving in the first session evoked the largest responses. CONCLUSION: The data demonstrate that the HPA axis can be strongly activated by exposure to, and anticipation of, a phobic situation." [abstract and full text]
TAKE HOME MESSAGE: People with a driving phobia suffer measurable physiological stress which starts in anticipation of the driving session and lasts for some time afterwards.
I'm sorry, but anyone suffering from a phobia can feel for themselves the racing heart rate, sweaty palms and all the classic symptoms of a physiological stress response. So even after reading the introduction to this paper (which outlined previous studies that had question the existence of a full stress response as part of phobic anxiety) I am having some trouble seeing this as a matter that was in an serious doubt. Inconsistent results are most likely caused by the fact that accurately measuring cortisol is a relative skilled task. Also cortisol is an good measure or stress experience over the course of minutes or hours, and people experiencing chronic stress might not show normal responses.