This study examined whether repetitive exposure to an irritant stimulant leads to desensitization and whether such modulation influences the psychological or the physiological response to that chemical. Subjects were exposed to acetic acid vapor in their home environment. Before, during, and after 3 weeks of daily exposure, the authors obtained electrophysiological recordings at peripheral and central levels in combination with psychophysical responses to acetic acid and acetone. Responses to acetic acid decreased during and following exposure. This did not generalize to the control irritant. Thresholds measured 1 year following exposure returned to baseline levels. In summary, repetitive exposure to an irritant vapor results in a specific desensitization to irritancy from that chemical, which appears to originate at a peripheral level.