Loeffler's syndrome is a rare form of pulmonary eosinophilia, with symptoms that are usually transient, self-limited, and benign lasting less than a month (usually 6-12 days). The etiology of Loeffler's syndrome is thought to be primarily an allergic reaction to the pulmonary migration of helminth larvae, specifically roundworm (A. lumbricoides), hookworm, and strongyloidiasis.