Conversely, both the COPD (0.80–0.64 pg/mL, p = 0.025) and asthma (0.06–0.05 pg/mL, p = 0.007) groups exhibited significantly lower levels of interleukin-4 (IL-4) and interleukin-6 (IL-6) in EBC following hydrogen inhalation. Here, IL4 is linked to chronic obstructive pulmonary disease.