Acute Asthma Exacerbation: This is often the most common cause of acute SOB, especially in patients with a history of asthma. It is characterized by reversible airflow obstruction, bronchospasm, and inflammation.

Chronic Obstructive Pulmonary Disease (COPD) Exacerbation: Similar to asthma, but typically seen in patients with a history of smoking or long-term exposure to lung irritants. It involves progressive airflow limitation.
Pneumonia: An infection of the lungs that can cause acute SOB, especially in older adults or those with compromised immune systems. Symptoms include fever, cough, and chest pain.
Pulmonary Embolism (PE): A blood clot in the lungs that can cause sudden onset of SOB, chest pain, and possibly syncope. It's more common in patients with risk factors such as recent surgery, immobilization, or cancer.
Heart Failure: Acute decompensated heart failure can lead to SOB due to fluid buildup in the lungs (pulmonary edema). It's often accompanied by leg swelling and fatigue.

Myocardial Infarction (MI): Although chest pain is the hallmark symptom, some patients, especially women and diabetics, may present with SOB as the primary symptom.
Pneumothorax: A collapsed lung that can cause sudden, severe SOB and chest pain. It's a medical emergency requiring immediate intervention.
Anaphylaxis: A severe, life-threatening allergic reaction that can cause SOB, among other symptoms like rash, swelling, and hypotension.

Pulmonary Lymphangitic Carcinomatosis: A rare condition where cancer spreads to the lymphatic vessels in the lungs, causing SOB.
Eosinophilic Pneumonia: A rare inflammatory condition characterized by eosinophilic infiltration of the lungs, leading to SOB and other respiratory symptoms.
Goodpasture Syndrome: A rare autoimmune disease that affects the lungs and kidneys, causing SOB, hemoptysis, and renal failure.