What do we know about the recent rise in allergies?

Over the past few decades, researchers have struggled to answer the question, "Why has the incidence of allergic diseases increased so rapidly in developed countries?" This has led to various theories ranging from the "hygiene hypothesis" which was first proposed back in the early 1990s, to recent studies of the "microbiome." Even most physicians and scientists not in these fields have now become at least somewhat familiar with these concepts. And these terms are even becoming part of our household vocabulary.

Which is a good thing…or is it? The hygiene hypothesis basically tries to explain that the increase in allergies comes from having better hygiene. Soaps, flushing toilets, hand washing, disinfectant solutions, and better living conditions gives the body less infections to fight, and the immune system is bored out of its wits. It has to do something, right? So what about allergies? There is a saying that the immune system abhors a vacuum, and this is precisely where this concept can be applied.

The "microbiome" refers to the combined genetic material of the microorganisms in a particular environment. In fact, we live in synergy with many other creatures on this earth, including various bacteria, viruses, fungi and other supposedly "infective agents." Many bacteria and viruses cause disease, but others are harmless. Some of these microorganisms live symbiotically within our bodies, and may in fact, be a part of how we maintain our health, or possibly lack of health.

The microbiome patterns which promote health are far from being fully known – so any discussion of how one can manipulate one's microbial renters, is futile. One of the clinical outcomes of all this developing knowledge is that we believe that probiotics are beneficial to health, and we now spend millions or billions of dollars every year on these products. But the truth is that while probiotics probably do support human health, the entire mechanisms by which this occurs from a biological or biochemical standpoint are far from fully known.

This brings us to a recent study on hand washing dishes versus using a dishwasher.  Swedish researchers reported that allergies were much less prevalent in families that "usually" washed dishes by hand, instead of using a dishwasher. Before you auction off your expensive KitchenAid, we should probably take a look at the study and its design. Firstly, the study was completely questionnaire based, and the participants were all 7 to 8 years of age. This means that the diagnosis of allergies was not made by a physician.

Secondly, the question used to determine if dishes were hand washed or if a dishwasher was used was "How do you usually wash the dishes?" Well, what exactly does that mean? Is it more than 50 percent of the time, all of the time, 75 percent of the time, or 40 percent of the time? And what if you ate out in a restaurant? The authors tried to relate the method by which dishes were washed with the amount and type of bacteria present on the dishes. But these data were from another study, not this one. In addition, there was no information on how the dishes were stored, how long they sat before being used, and the presence of other unknown factors that could have affected the outcome of the study.

The authors used a powerful statistical tool called "principal component analysis" to achieve statistical significance (which means the results were less likely to be by chance) in this study. But one should be wary of complex statistics – with the proper tools, a good statistician can make almost anything appear significant.

What should you do now? I already discouraged you from ditching your dishwasher, but is there any truth to this whole Palmolive versus Cascade dilemma? The answer, at least as of today, is that yes, our exposure to bacteria and other microorganisms almost certainly plays a role in health. But we really do not know the whole story just yet. Ongoing research to determine the respective roles of genetics and the environment is being conducted not just in allergic diseases, but also in many other diseases..

However, it will be decades before we can tell our patients and families exactly what kids should be exposed to (or avoid), and when, where and how. One should also remember that allergic diseases vary from one person to another and what is the right solution for one person may not be at all helpful for the next allergy sufferer. So for now, I wouldn't advise that you change anything that you are doing with regard to washing dishes, at least not based on this one, single study. But…stayed tuned!

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