Subgroup analysis indicated that asthma adults showed higher IL‐33 level in serum, compared to HCs, whereas no significant difference in IL‐33 level in serum was showed between asthma children and HCs (adults: SMD 2.17, 95% CI 1.09−3.25; children: SMD 1.81, 95% CI −0.11 to 3.74). Here, IL33 is linked to asthma.