When Sweet Turns Toxic: Acute Hypersensitivity Pneumonitis from a New Flavored Heated Tobacco Product: A Case Report

We report a 45-year-old man who developed acute hypoxemic respiratory failure after switching flavors of a heated tobacco product (HTP). Chest radiograph and computed tomography showed diffuse ground-glass opacities with upper lobe predominance. Bronchoalveolar lavage revealed lymphocytosis (46%) and lipid-laden macrophages, while infectious and autoimmune causes were excluded. Based on the 2022 Japanese Respiratory Society Hypersensitivity Pneumonitis Guideline, a diagnosis of acute non-fibrosing hypersensitivity pneumonitis induced by HTPs was made. Corticosteroid therapy resulted in rapid clinical and radiologic improvement. This case highlights HTPs as a potential trigger of acute hypersensitivity pneumonitis.