The use of oxygen as part of the process for generating metabolic energy produces reactive oxygen species.  In this process, the superoxide anion is produced as a by-product of several steps in the electron transport chain .  Particularly important is the reduction of coenzyme Q in complex III , since a highly reactive free radical is formed as an intermediate (Q · − ). This unstable intermediate can lead to electron "leakage", when electrons jump directly to oxygen and form the superoxide anion, instead of moving through the normal series of well-controlled reactions of the electron transport chain.  Peroxide is also produced from the oxidation of reduced flavoproteins , such as complex I .  However, although these enzymes can produce oxidants, the relative importance of the electron transfer chain to other processes that generate peroxide is unclear.   In plants, algae , and cyanobacteria , reactive oxygen species are also produced during photosynthesis ,  particularly under conditions of high light intensity .  This effect is partly offset by the involvement of carotenoids in photoinhibition , and in algae and cyanobacteria, by large amount of iodide and selenium ,  which involves these antioxidants reacting with over-reduced forms of the photosynthetic reaction centres to prevent the production of reactive oxygen species.  
Of the reported cases of anaphylaxis attributed to Xolair, 39% occurred with the first dose, 19% occurred with the second dose, 10% occurred with the third dose, and the rest after subsequent doses. One case occurred after 39 doses (after 19 months of continuous therapy, anaphylaxis occurred when treatment was restarted following a 3 month gap). The time to onset of anaphylaxis in these cases was up to 30 minutes in 35%, greater than 30 and up to 60 minutes in 16%, greater than 60 and up to 90 minutes in 2%, greater than 90 and up to 120 minutes in 6%, greater than 2 hours and up to 6 hours in 5%, greater than 6 hours and up to 12 hours in 14%, greater than 12 hours and up to 24 hours in 8%, and greater than 24 hours and up to 4 days in 5%. In 9% of cases the times to onset were unknown.