When patients were stratified according to the status of atopy, the serum IL-31 levels in patients with allergic asthma were higher than those in patients with nonallergic asthma (157.7 [132.5–184.7] pg/ml versus 63.4 [39.1–102.3] pg/ml; p < 0.05) and controls (157.7 [132.5–184.7] pg/ml versus 52.5 [38.5–62.7] pg/ml; p < 0.001) (Fig. 1B). Here, IL31 is linked to asthma.