Hydrogen peroxide is a chemical commonly used as a household antiseptic for cleaning and disinfecting. No cases of acute hydrogen peroxide inhalation-induced lung injury are previously described. We present a case of acute chemical pneumonitis caused by mixing hydrogen peroxide in a nighttime continuous positive airway pressure device's humidifier used for obstructive sleep apnea to prevent COVID-19 infection. The patient endorsed mixing hydrogen peroxide with distilled water in his nighttime continuous positive airway pressure device's humidifier at a ratio of 1:3-1:2 for the previous week before admission based on a friend's advice in preventing COVID-19. The presenting chest X-ray showed new multifocal consolidations with interstitial markings and alveolar edema throughout both lungs. Chest computed tomography (CT) imaging demonstrated multifocal, bilateral, hazy consolidations with increased interstitial markings and bilateral pleural effusions. The patient was subsequently initiated on systemic glucocorticoid therapy, significantly improving hypoxemia and dyspnea. Inhalation of hydrogen peroxide may produce acute pneumonitis distinct from what has been described previously with chronic inhalation. Given this case, systemic glucocorticoid therapy may be considered a viable treatment option for acute hydrogen peroxide-associated inhalation lung injury causing pneumonitis.