In contrast, unchallenged 12‐ and 18‐month‐old Cc16−/− mice had greater small airway fibrosis than unchallenged 6‐month‐old Cc16−/− mice, but small airway fibrosis did not differ between 12‐ and 18‐month‐old Cc16−/− mice. This evidence concerns the gene SCGB1A1 and fibrosis.