This trial aims to evaluate the safety, tolerability and efficacy of hUC-MSC-sEV-002 nebulizer in patients with allergic rhinitis and asthma. It consists of two parts: ① Single-center dose exploration (The Affiliated Hospital of Qingdao University): A 3+3 escalation design will test three doses (1×10⁸, 1×10⁹, 1×10¹⁰ particles/mL) to determine the maximum tolerated dose (MTD).Three subjects will be enrolled in each dose group. If no Dose-Limiting Toxicity (DLT) is observed among the 3 subjects, the study may proceed to the next dose exploration. If 1 out of the 3 subjects experiences DLT, an additional 3 subjects will be enrolled in the same dose group; the study may move to the next dose exploration only if no DLT is observed in these additional 3 subjects. If more than 1 out of the 3 subjects develops DLT, the previous dose group will be defined as the MTD. A total of at least 9 and at most 18 subjects will be recruited for this clinical trial. ② Multi-center case expansion: Participants will be randomized 2:1 to hUC-MSC-sEV-002 or placebo groups for efficacy comparison.Eligibility criteria: 18-60 years old; moderate-to-severe allergic rhinitis (ARIA guidelines) with positive inhaled allergen skin test; asthma diagnosed per GINA 2022; signed informed consent.Intervention: Nebulization once daily (5 times/week, 2 weeks, 10 doses total). Follow-up visits at baseline, Week 2, 4, 12, 24, including symptom scales, lung function tests, nasal endoscopy, nasal exhaled nitric oxide test, chest X-ray, blood tests, and electrocardiogram. The trial is approved by the Medical Ethics Committee of The Affiliated Hospital of Qingdao University (No. QYFYEC2025-192). Participants may withdraw anytime without affecting medical care. Study period: Aug 2025-Aug 2027. Sample size: 9-18 for Part 1; Part 2 size based on Part 1 results.