Eosinophilic pneumonia is characterized by massive eosinophil accumulation in the alveoli and interstitium driven by IL-5 and eotaxin-mediated chemotaxis. Eosinophils release cytotoxic granule proteins (major basic protein, eosinophil peroxidase) that directly damage alveolar epithelial cells and basement membranes. Acute eosinophilic pneumonia (AEP) presents with rapid-onset respiratory failure, often in new smokers or after environmental exposure. Chronic eosinophilic pneumonia (CEP) follows a more indolent course with characteristic peripheral pulmonary infiltrates (photographic negative of pulmonary edema).