FeNO levels in healthy children depend on several non-disease-related factors, such as age, gender, height ethnicity, genetics, self-reported atopy, allergic sensitization, total IgE, time of testing, infections, a nitrate-rich diet, exercise, smoking, ambient nitric oxide, time of day and season, and environmental pollution [18, 34, 35]. The gene discussed is IGHE; the disease is infection.