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We are concerned by the recent publication of a randomised clinical trial in your journal, in which smoking parents were asked to continue smoking in the presence of their children for 6 months to evaluate if secondhand smoke (SHS) exposure increased the risk of bruxism.1 It is surprising that after acknowledging that SHS is “…a serious public health threat” with a large impact on children's health, ranging from respiratory affections to cardiovascular damage, authors conducted a study in which:“The smoking members of the families in group 1 were asked not to smoke in the presence of the child for a period of 6 months, while those in group 2 were asked not to change their smoking habits.”

What would have happened if a parent in group 2 had decided to quit smoking during follow-up? Would the investigators have encouraged him/her not to, or to wait until the end of the study? The active involvement of researchers in the decision to expose children to SHS contravenes the Helsinki declaration, since “…the well-being of the individual research subject must take precedence over all other interests”.2 Preventing family members from stopping smoking and actively seeking children to be exposed to a dangerous pollutant is reckless, as the benefits of knowing if SHS is a risk factor for bruxism cannot overcome the dangers of exposing children to SHS or the benefits of quitting. A reasonable approach to address the research question posed by the authors would have been to take an observational stance, developing the most effective intervention possible to eliminate SHS exposure at home for all children, closely monitoring bruxism and SHS exposure levels at home over time, and using each child as its own control. The methodological disadvantages associated with this approach would have been clearly balanced by its adherence to the Helsinki declaration.

As we move forward in eliminating SHS exposure, it is imperative that researchers, ethical committees, reviewers and scientific journals remain aware of the ethical implications of research, so our ends are met by our means. Failing to do so undermines participants' health and the global movement towards SHS elimination. Considering children's high vulnerability and inherent risks from SHS, we cannot think of a single research question that could justify actively seeking exposing children to SHS or preventing parents from stopping smoking to provide a healthier environment for themselves and their families. Although each study requires and individual assessment of the risk-benefit ratio, as a general rule, experimental studies involving exposure to SHS should be discouraged, preferring observational designs built upon the premise that all efforts will be made to support smoking cessation and eliminate SHS.