How Tar from Tobacco Smoke Damages Lungs and Causes COPD

Tar—the sticky, brown residue from combusted tobacco—is the primary driver of smoking-related lung damage.

Mechanisms of Injury

• Airway coating: Tar deposits on bronchial epithelium → ciliary paralysis → impaired mucociliary clearance.
• Inflammation: Tar constituents (PAHs, nitrosamines, reactive oxygen species) activate macrophages/neutrophils → protease/elastase release → alveolar wall destruction (emphysema).
• Mucous gland hyperplasia: Chronic bronchitis phenotype (cough/sputum ≥3 mo/yr × 2 yr).
• Carcinogenesis: DNA adducts → mutations in TP53, KRAS, EGFR → lung cancer.
• Small airway fibrosis: Obliterative bronchiolitis → fixed airflow obstruction (COPD).

Clinical Consequence

Tar accumulation narrows airways, reduces elastic recoil, and creates ventilation-perfusion mismatch → dyspnea, exercise intolerance, respiratory failure. Cessation halts progression; some inflammation reverses, but structural damage (emphysema) is permanent.