This is a very good observation. However, we must keep in mind that the CO2 challenge is a model of panic though to trigger symptoms by momentarily activating a system that monitors acute acidosis (such as that produced by suffocation). Therefore the panic reaction to this maneuver is also very brief (seconds rather than minutes) when compared to natural spontaneous panic attacks. During provocation procedures using CO2 high doses are necessary to provoke a reaction. Such is the case of either a couple of breaths of 35% CO2 or a continuous inhalation of lower concentrations for several minutes. Due to the nature of CO2 and the efficiency of the bicarbonate buffer system, pH homeostasis is rapidly restored once these procedures are terminated. In this scope, the CO2 increases produced by breathing in a paper bag for a few minutes are usually too small to exacerbate panic. In any case, rebreathing in a paper bag to treat the respiratory alkalosis during acute anxiety may not advisable for a number of reasons. In prolonged rebreathing the increases of CO2 can potentially be enough to exacerbate panic symptoms and moreover dangerously lead to hypoxemia. Additionally, one study suggests that paper bag re breathing has no specific effect on the alleviation of symptoms produced by hyperventilation. Coaching patients to take slow and shallow breaths may give the same results with less potential adverse effects.