We have read with interest the article by Bedolla-Barajas et al. [1] and we believe the lack of association between passive smoking and asthma might be a consequence of the way the variable was measured. They defined passive smoking as follows:

"smoking was considered as passive when one or more cigarettes were consumed by one or by both parents in the presence of the children". We would like to highlight some factors that could have been taken into count when defining this variable: time of smoking, frequency and number of cigarettes.

Radic et al. [2] established a strong correlation between pediatric asthma and smoking families in a cross-sectional study in children between 4 and 17 years old. They explored the habit of smoking in the parents by asking them about the age of onset and the frequency of smoking. They found that the parents of children with asthma started smoking at an average age of onset of 15 to 18 years ago. Similar findings were also evidenced in another cross-sectional study by Irvine et al. [3], who included age of onset, frequency of smoking and the presence of other active smokers apart from the parents.

In addition, Suárez López de Vergara et al. [4] found association between the amount of cigarettes parents smoke and asthma. They add in the parent's questionnaire the number of cigarettes they usually smoke and reported a cutoff point of 10 cigarettes to be related with children with asthma and exacerbations. They evidenced this by measuring cotinine levels in children.

To sum up, the title of the reviewed study may lead to a misunderstanding. It affirms there is no relation between asthma and 'passive smoking', we believe the latter requires further study in order to establish whether there is association or not with asthma in Mexican children.