Tag Archives: hygiene hypothesis

Any proof for hygiene hypothesis by lockdown babies?

It is an interesting question – does social distancing influence later allergy ? Lawler et al. in November 2021


report the impact of COVID‐19 lockdown in 365 Irish babies at 6 months of age enrolled in the CORAL study. These were a subset of 3773 infants born in two participating major maternity hospitals in Dublin between March and May 2020. Unfortunately only 10% of children participated, so families were self-selected.  Allergic rhinitis was common in both mothers (36%) and fathers (30%) which is higher than reported by Allergy Ireland (26%) and explained by the authors that parental allergy is “higher than the general population, which may have contributed to parental desire to enrol in this study.”

A follow-up in March 2022 in 344 children consecutively shows higher food allergy (4.7% vs 3.5%, NS) when compared to an earlier cohort (BASELINE 2008). Atopic dermatitis increased of 15.5% in the BASELINE study to 25.3% in CORAL (no P reported) which is not unexpected given the interest of parents in an allergy study.

Nevertheless the authors needed now to analyze their stool samples sitting in the shelves. This is the content of  the March 2023 preprint that has just been published. There may be some association of some bacteria with atopic dermatitis but in the end it is a useless result as the strongest risk factors for atopic dermatitis – parental history and/or FLG mutations – are missing from the presented models

At the end we can safely assume that the 2020 lockdown did not have any influence on allergy prevalence in Ireland.

Hygiene hypothesis hyperbole

Having written about the hygiene hypothesis, I missed a PNAS News feature even some years ago.

Again: The hygiene hypothesis was not born by David Strachan and well, there are more cracks of the hygiene hypothesis.

“The trouble is, as soon as you use the words ‘hygiene hypothesis,’ the word hygiene prejudges what the cause is,” says Bloomfield. To the public, “hygiene” is interpreted as personal cleanliness: washing hands, keeping food clean and fresh, sanitizing the home. However, because the hypothesis has been largely uncoupled from infections, the idea that we need to be less hygienic is wrong. Relaxing hygiene standards would not reverse the trend but only serve to increase the risks of infectious disease, says Bloomfield. The term “hygiene hypothesis” also fails to incorporate all of the other factors now linked to the increase in immunoregulatory diseases.

I expect that five years after mandating “super hygiene” during COVID-19 we can finally bury the hygiene hypothesis.

The bullshit asymmetry principle aka Brandolini law

I agree immediately to the fact, that the amount of energy required to refute bullshit is an order of magnitude bigger than to produce it.

The kinds of people who bullshit are more likely to be the kinds of people who misrepresent evidence, avoid correcting their errors, and intimidate dissenters, so at some point the people who could shoot down the bullshit might decide it’s not worth the trouble: Why bother fight bullshit if the bullshitters are going to turn around and personally attack you? From this standpoint, once bullshit becomes “too big to fail,” it can stay around forever.

The bullshit asymmetry principle

Can criticial thinking been teached?

Yes, it can.

Already in 2017 there was a Lancet paper with the super-long title “Effects of the Informed Health Choices primary school intervention on the ability of children in Uganda to assess the reliability of claims about treatment effects: a cluster-randomised controlled trial”. The paper is extensively discussed at vox.com

Andy Oxman is obsessed with the study of bullshit health claims and how to prevent them from spreading.
For decades, he’s been trying to find ways to get adults to think critically about the latest diet fads, vaccine rumors, or “miracle cures.” But he realized these efforts are often in vain: Adults can be stubborn old dogs — resistant to learning new things and changing their minds.

So not only Germany but also Uganda has its own bullshit hypothesis.

Harmed by the hygiene hypothesis

A new paper by a British-Kazakhstan-Armenian group nicely summarizes why we need good hypothesis papers.
As a deterring example they use the hygiene hypothesis

the hygiene hypothesis that was originally proposed by David Strachan in 1989. David Strachan studied the epidemiology of hay fever in a cohort of 17,414 British children and concluded that declining family size and improved personal hygiene had reduced the chances of cross infections in families, resulting in epidemics of atopic disease in post-industrial Britain. Over the past four decades, several related hypotheses have been proposed to expand the potential role of symbiotic microorganisms and parasites in the development of human physiological immune responses early in life and protection from allergic and autoimmune diseases later on.

I agree with the description although David never claimed to be the first author writing about the hygiene hypothesis. When I spoke to him the last time London he wasn’t even happy with this popularity.

The chain certainly started also much earlier than 1989 with “continuing activity of an immune system made redundant by man’s cleanliness” (Godfrey, 1975) continued with Gerrard 1976, Frick 1986, Busse, 1989 until David Barker argued in 1985 that there is a “decreased incidence of infection among children, especially in wealthier families, that changed their pattern of immunity”.

The harm inducted by the hygiene hypothesis is described as

The misunderstanding of the hygiene hypothesis that primarily aimed to shed light on the role of the microbiome in allergic and autoimmune diseases resulted in decline of public confidence in hygiene with dire societal implications, forcing some experts to abandon the original idea. Although that hypothesis is unrelated to the issue of vaccinations, the public misunderstanding has resulted in decline of vaccinations at a time of upsurge of old and new infections.

I fear the authors are right – some people may have been harmed by the hygiene hypothesis leading them back in the pre-Semmelweis era.

Forget the hygiene hypothesis until there is a good study

A new paper in PLoS Negl Trop Dis this week reports

The hygiene hypothesis is accepted by many in the global scientific community […] However, aspects of this hypothesis are based on assumptions that may not fully account for realities about human helminth infections. Such realities include evidence of causal associations between helminth infections and asthma or inflammatory bowel disease

Talking about realities may help proponents of the hygiene hypothesis who are stuck in a never ending loop publishing  observational studies.

Even the NEJM contributes to the hygiene hysteria hype this week. Although the allergic rhinitis prevalence isn’t so much lower in old order Amish (who are even a heterogenous group), the difference to Hutterite is being highlighted. I do not even understand the study design here as it is neither cross-sectional, nor case-control nor cohort study. Is it just an exposure description in two different groups?  Conclusions like

sustained microbial exposure was also reflected in the phenotypes of peripheral innate immune cells in the Amish.

are strange if we believe that we humans carry more bacterial than human cells. And every smoker encounters a 120fold endotoxin concentration compared to ambient air – without getting rid of asthma or allergy.

The results of our studies in humans and mice indicate that the Amish environment provides protection against asthma

is certainly wrong – nobody knows if this is an environmental or genetic or iatrogenic factor. The key finding is IRF7 expression but unfortunately IRF7 plays a critical role in the innate immune response against viruses – and not bacteria/endotoxin…

Another challenge of the hygiene hypothesis

The hygiene hypothesis usually assumes an “underemployed” system that is directed against self-defined allergen targets – a rather mechanistic view of a half filled barrel. A new Nature paper on memory CD8 T-cells now explains why this view is rather odd Continue reading Another challenge of the hygiene hypothesis

The end of the hygiene hypothesis

The authors put a question mark at the end of the above statement while I would not hesitate to put an exclamation mark there. Writing this as a comment to a new study in the IJE they summarize the evidence that the “epidemics” of asthma in Western countries has begun to decline – as hygiene standards are not declining this might indicate the end of the hygiene hypothesis. Continue reading The end of the hygiene hypothesis