Allergic rhinitis and asthma share the 'one airway, one disease' theory — both upper and lower respiratory tract allergic inflammation. Untreated rhinitis develops into asthma in 30–40% of cases. Korean medicine prevents this progression by treating allergic constitution at its root: ① rhinitis treatment (1–3 months), ② constitution improvement herbs (3–6 months), ③ immunity boost (long-term). Early treatment is the best asthma prevention.