Inclusion Criteria:  (1) aged 18 to 60 years; (2) only had a positive response to Der p and Der f but no other inhalant allergens based on EUROline Allergy Diagnostics (Beijing Oumeng Biotechnology Co., Ltd., Beijing, China). Meanwhile at least Der p -specific IgE (sIgE) in serum of was ≥ 0.7 kU/l (CAP Pharmacia, Uppsala, Sweden) using ImmunoCAP system (Pharmacia, Uppsala, Sweden) regardless of the result of Der p -specific IgE in serum; (3) had reached cluster SCIT maintenance period and the overall treatment time was more than 1 year but less than 2 years; (4) hope to continue to complete the entire treatment and have good compliance.  Exclusion Criteria:  (1) diagnosed as asthma based on the guidelines of the Global Initiative for Asthma(13); (2) had Grade II or above systemic adverse reactions occurred in the past SCIT period.