A new study claims that men who used snus during puberty may pass on a higher risk of asthma and allergies to their children. But a prominent researcher says the study suffers from serious methodological flaws.

The study, published in the International Journal of Epidemiology and funded by Sweden’s Hjärt-Lungfonden (Heart-Lung Foundation), followed 1,090 father-child pairs using two long-running Swedish health surveys. 

Researchers found that children of fathers who started using snus in their teenage years (89 fathers in total) had a higher rate of allergic asthma, asthma symptoms, chronic bronchitis, and eczema compared with children of fathers who never used snus. 

No such pattern showed up for fathers who started snus later, as adults. 

The study’s authors suggest that snus use during puberty may trigger changes in sperm cells that get passed down to children.

However, Dr. Arielle Selya, a Senior Scientist at Pinney Associates who studies tobacco harm reduction, says the study suffers from methodological shortcomings, concluding the data is far too thin to support the claims being made about it.

Premise ‘doesn’t seem plausible’

Following a review of the study and its methodology, Selya first expresses concern over its basic premise.

“It doesn’t seem plausible at all,” she says. 

“Snus use doesn’t involve the lungs or airways in any way, so it’s hard to see how it could cause respiratory problems in someone’s future children.”

That doesn’t mean the numbers in the study are wrong, she stresses – but it does mean researchers need an unusually strong case to explain why an association would exist at all, and that’s where the study runs into trouble.

Too few other explanations ruled out

The researchers use a fairly advanced statistical method to account for other possible explanations that could explain why fathers’ snus use is associated with respiratory symptoms in offspring, but Selya says this can’t make up for how few explanations were actually included. 

“The method they used looks sophisticated, but it can’t fix the underlying problem, which is that they only checked for a small handful of other possible explanations,” she explains.

The study mainly accounted for the father’s own childhood asthma, whether he smoked, the grandparents’ education level, and a few basic facts about the children themselves. 

However, the authors have ignored or left out several other relevant factors, she points out.

Many should be considered ”obvious” candidates: the mother’s respiratory health, whether the mother smoked, exposure to air pollution, or even mold in the home.

Allergies, not asthma in general

One detail in the results stands out to Selya. The link to snus showed up mainly for allergy-related asthma and eczema – not for asthma overall. 

“To me, that points toward allergic or immune-related conditions, not respiratory disease specifically,” she explains.

If that’s the real pattern, she argues, an entirely different set of explanations becomes relevant — ones the study doesn’t touch at all. 

Things like whether the family has a pet, or even how dishes get washed at home, are both established factors linked to a child’s risk of allergies.

Smoking, measured too loosely

The study did adjust for whether fathers smoked, which might seem like the obvious factor to control for. But Selya says the measurement was too rough to do its job. 

Fathers were only recorded as having smoked before or after puberty, not whether they were still smoking later in life, when their children were growing up.

That distinction matters, she says, because heavy, long-term smoking could mean a father passed down genes linked to smoking, or that his children were simply exposed to smoke at home. 

“Because cigarette smoking is more common among men who also used snus, that could explain why offspring have higher respiratory symptoms – but the blame ends up falling on snus instead,” she says.

The checks that weren’t run

The study’s authors also ran several additional tests to see whether their results held up under different conditions – removing children who used snus themselves, for instance, or whose fathers had hay fever. 

Selya warns these tests don’t address the study’s real weak points. 

The researchers never checked what happened if they removed children whose fathers never smoked regular cigarettes, or whose parents had asthma themselves.

The checks, she says, simply don’t target the issues that matter most.

”Sensitivity analyses are a good idea, but the ones chosen here aren’t relevant to the key issues,” says Selya.

Correlation without cause; association, not proof

To illustrate her concern, Selya points to a detail buried in the study’s own data: grandparents’ education level lines up with whether the father used snus. 

But a man’s teenage snus use obviously can’t have affected his own parents’ education years earlier. 

It’s a pattern in the data with no possible causal story – yet, she argues, similarly weak patterns elsewhere in the paper are used to support much stronger conclusions than the evidence can carry.

Nevertheless, Kristina Sparreljung, Secretary General of the Swedish Heart and Lung Foundation, didn’t hesitate to draw rather strong conclusions what the study meant for the potential effects of nicotine. 

“The results are worrying and indicate a link between exposure to tobacco and nicotine early in life and consequences much later – even for the next generation,” she said in a statement accompanying the study’s release.

But for Selya, who also consults for Juul Labs and serves as a scientific advisor to the Global Forum on Nicotine (GFN), the study is a warning, not about the perceived dangers of nicotine, but of what happens when an association in the data is misinterpreted as a cause. 

“If offspring’s snus use, father’s snus use, and father’s asthma are all correlated, it would be absurd to claim that offspring’s snus use caused their fathers’ asthma, yet the claims in this paper are based on the same quality of evidence,” she explains.

Without ruling out far more of the everyday factors that tend to run in families – allergies, smoking habits, home environment – claims that a father’s snus use harms his children’s health remain, in her view, unproven.

“The severe flaws and limitations in this study do not come close to justifying the strong language and confident conclusions made by Sweden’s Heart-Lung Foundation,” says Selya.

“In fact, this kind of messaging will likely increase misperceptions that all nicotine products are equally harmful – misperceptions that, unfortunately, are keeping many people smoking much more harmful cigarettes. Health authorities bear a responsibility for accurate messaging that corrects rather than worsens these record-high misperceptions.”