Environmental tobacco smoke (ETS) in the home is a major preventable health problem for children around the world. In children, ETS exposure (passive smoking) has been shown to be particularly associated with respiratory infection, especially lower respiratory tract infection (LRTI).^1–3 Exposure intensity of ETS among children shows a strong correlation with indoor parental and, especially, maternal smoking, the number of cigarettes smoked, the number and volume capacity of the rooms where cigarettes are smoked and individual metabolic diversities.⁴ The use of cotinine, a major metabolite of nicotine, as a biological marker of smoke absorption has been suggested as an approach to strengthen the evidence of the relation between passive …