Corticosteroids, including prednisone, are a class of powerful drugs that reduce inflammation and suppress the immune system. They are prescribed for a wide variety of conditions, including rheumatoid arthritis (RA) and lupus, as well as multiple sclerosis, some types of cancer, asthma and skin rashes – including those caused by poison ivy. They can be prescribed short-term – until a rash clears up or until another drug can take effect, for example – or they may be used long-term. Corticosteroids come in skin creams, injections and inhaled forms; however, this study examined only people who took them orally.
Glucocorticoids are potent anti-inflammatories, regardless of the inflammation's cause; their primary anti-inflammatory mechanism is lipocortin-1 (annexin-1) synthesis. Lipocortin-1 both suppresses phospholipase A2 , thereby blocking eicosanoid production, and inhibits various leukocyte inflammatory events ( epithelial adhesion , emigration , chemotaxis , phagocytosis , respiratory burst , etc.). In other words, glucocorticoids not only suppress immune response, but also inhibit the two main products of inflammation, prostaglandins and leukotrienes . They inhibit prostaglandin synthesis at the level of phospholipase A2 as well as at the level of cyclooxygenase /PGE isomerase (COX-1 and COX-2),  the latter effect being much like that of NSAIDs , potentiating the anti-inflammatory effect.