Regarding the letter sent to the editor of Asia Pacific Allergy Journal, motivated by our recent article, "Asthma in Mexican school-age children is not associated with passive smoking or obesity", where it is thought that the title may lead to misinterpretation, to state that there is no association between how it was evaluated in passive exposure to cigarette smoke and asthma in Mexican children, our comments are as follows:

The observations made about it by the author of the letter to the editor, initially are pertinent, especially if it were to evaluate the effect of passive smoking and asthma severity, just as they do Radic et al. [1] and Suárez López de Vergara et al. [2]. The first, mainly aimed to assess the impact of exposure to cigarette smoke on the health of children with asthma, for it, they asked about smoking habits of parents in a way very similar to ours, they were able to show a significant association between the number of respiratory infections, asthma exacerbations and passive smoking during certain periods of life of children, but we must consider that these authors only included those cases where children who had asthma with moderate and severe symptoms, a condition that makes them more vulnerable not only to cigarette smoke, but to any other external irritants also. In the second study, the authors clearly state that their purpose is to assess whether exposure to tobacco smoke in the homes of children modifies asthma severity, this time, passive smoking was quantified in a much more detailed way, even so the results were contradictory, since they found increased severity of asthma in children with passive smoking at the time of the survey, it increased the severity of asthma in the year before the study, but there was no significant association between asthma severity usual in the last year and exposure to tobacco smoke, likewise there was no significant association between the number of cigarettes to which the child is exposed and the severity of asthma; equally inconsistent behavior was documented in respiratory function tests. Moreover, in the scientific literature worldwide we can find various definitions of smoking. Many of them take into account the amount, frequency and duration (in years or months) consumption of cigarettes per day. However, establishing an operational definition only to be applied in different populations is particularly difficult. For example, in the past ten years, Mexico has made a series of two important surveys that measure national smoking prevalence: the National Survey of Health and Nutrition (ENSANUT, for its acronym in Spanish) and the National Survey of Addictions (ENA, for its acronym in Spanish) [3-5]. Both used different operational definitions in part limiting the comparison of their results. The first defines smoking as the consumption of more than 100 cigarettes in a person's life [3, 4], while the second, defined as persons who reported having smoked in the year prior to the date of the interview [5].

In addition, passive smoking is defined in the ENA survey as a person who has never smoked but who lives daily with at least one smoker in their home, classroom or at work [5]. Our research took this definition and adapted to the context of children given their age, have not yet started smoking, but who may be in contact with someone at home (parent or both) who smoke daily. "Smoking was considered as passive when one or more cigarettes were consumed by one or by both parents in the presence of their children," is a definition that assumes that, in the event that one or both parents are smokers, they would smoke on a daily basis and sustained a smoking habit. In Mexico, the average consumption of cigarettes by adults is greater than 6 cigarettes and 11.4% reported that their first cigarette was consumed within 30 minutes of waking up, also the main site of exposure to environmental smoke of tobacco is at home [5].

Recently, our group showed through a cross-sectional, population-based study, conducted a sample in late adolescents, that there was no statistically significant association between active or passive exposure to cigarette smoke and the prevalence of asthma [6]. Consistent with our results, the findings are shown by another group of researchers in our country [7]. It is noteworthy that in both studies, the way to assess passive smoking was very similar. It seems that the effects of passive smoking are mostly linked with the severity of symptoms and the number of exacerbations, as was shown by Mannino et al. [8] in their report obtained from the Third National Health and Nutrition Examination Survey.

In conclusion, our findings must be interpreted strictly considering the way how the variable smoking was recorded, so the lack of consistency with the results of previous publications should encourage further studies in our country, in order to allow a comparison with other international studies.

We appreciate the comments made in our work, hoping to have cleared the doubts with it.