Long term passive exposure to tobacco smoke can be a cause of disease in sensitive non smokers, particularly in children of smoking mothers, who may suffer more frequently from respiratory tract infection, otitis media and chronic cough as well as exacerbation of pre-existent asthma. In adults, the relationship is less obvious. A slight but significant alteration of lung function has been observed. The increase in the incidence of lung cancer in non-smoking spouses (men and women) of smokers can be regarded as proven.