Outdoor germs and allergies

Colored picture of pollen grains from various plants, from Wikipedia

Most seem to find it normal. But I find it creepy: Something in our living environment makes many of us sick. Asthma, allergies and atopic eczema was rather rare before the second half of the 20th century. Now tens of percent of Westerners have allergic diseases, more than 40 percent in this study for example. The conditions are multiple times rarer in countries with low living standards. 

I'm a bit surprised that people don't care more about this. Obviously we are doing something differently than rural poor people. This something makes a large share of us allergic. Maybe the protective factor lies in the nastier parts of being rural and poor. If it turns out that rural poor people escape allergic disease because they suffer from intestinal worms or drink unclean water or unpasteurized milk, then we might not want to copy them. But if it turns out that some mostly harmless aspect of the lives of poor rural people makes them less susceptible to allergic diseases, then copying them would be a great idea. Efforts spent figuring out what keeps poor people from getting allergic diseases could pay off hugely.

The Amish and their cousins 

Statistics are messy, but within the First World, allergic disease seems to be more common in urban areas than in rural areas. Especially farm children are less allergic than the general population. More siblings, especially older siblings, seem to offer protection.

Until 1989, it was assumed that the increase in allergic diseases was caused by chemical pollution of the environment. In 1989 the hygiene hypothesis was launched. At first, researchers looked at the number of infections a child went through. The results were confusing. Some infections actually seemed to increase the risk of allergies instead of decreasing it. The hygiene hypothesis was subsequently developed into the old friends-hypothesis. What protects people from allergies might not be pathogens that make people ill, but microorganisms that we have evolved to tolerate. We tolerate them so well that we even need them. Through mouse studies, researchers have been able to point at some microorganisms that seem to be better than others at preventing allergies.

One interesting study seeking the causes of allergic disease compared a population of Amish farmers in Indiana to a Hutterite colony in South Dakota. The Amish and the Hutterites are closely genetically related. They both stem from anabaptist movements from German-speaking areas in the 16th century. Both still speak dialects of German. But their cultural weirdness pulled in slightly different directions. The Amish made rules against technology. Meanwhile, the Hutterites relied on advanced social engineering. While the Amish live in nuclear or extended families like most people, the Hutterites are agricultural socialists. They own and run high-tech farms in collectives of about 130-150 people. Among the Hutterites, houses are situated much further away from animals than among the Amish. 

The Amish had rather low levels of allergic disease. Among Amish farm children in Indiana, 5.2 percent had asthma and 7.2 percent had allergic sensitization. Meanwhile, among Hutterite farm children from South Dakota 21.3 percent had asthma and 33.3 percent allergic sensitization. The researchers analyzed dust from both Amish homes and Hutterite homes and concluded that there were less animal-related microorganisms in Hutterite homes. The barn dust didn't escape into Hutterite homes like it did into Amish homes.

This study indicates why living on a farm protects children against allergic disease. It is not because their fathers work with animals and soil. It is because they get into contact with the farm dirt themselves. If they don't, living on a farm doesn't help one bit.

Do we need to keep cows?

The Amish/Hutterite study is somewhat worrying for all of us who don't want to keep cows. Is barn-dust the only formula that protects against allergic disease?

In order to get some clues for that question, I searched for rates of allergic disease in a population that definitely doesn't hold cows: The Inuits. A comparison between people in Denmark, Greenland city of Nuuk and Ummannaq, a rural settlement in Northern Greenland showed the usual urban high income/rural low income pattern. The prevalence of at least one positive skin prick test was 22.8% in Denmark, 10.6% in Nuuk, and 6.4% in Ummannaq. The researchers explain the differences by different exposure to allergens: The Danes have a lot more pollen and dust mites.

But obviously, rates of allergic diseases also vary enormously between populations exposed to identical levels of pollen. One study from 2011 compares people from the Karelia region, which is divided in one Finnish side and one Russian side. The study looked at frequencies in allergic disease in both 1997 and 2007. On the Finnish side, allergic disease increased markedly during that period. On the Russian side, it didn't increase at all. In the early 2000's, in Russian Karelia only 2 percent of school-children in the study were sensitized to birch pollen compared with 27 percent in Finnish Karelia. Adult birth cohorts showed that among those born in the 1940s the sensitization to pollen and pets was at the same low level in both countries. Among people born in the late 1970s the difference was manifold. 

That is, something happened in Finland in the middle of the 20th century. Was it that Finns ceased owning cows? I think that happened much earlier. Far from every family in Finnish Karelia had a cow in the 1940s. And far from every family in Russian Karelia owned a cow in 2007. The study provides no information about the number of agricultural households, but according to Wikipedia the most important industries in Russian Karelia are forestry, mining, tourism, agriculture, fishing and paper manufacturing. Rural Russians tend to be poor, but in general they are not subsistence farmers. 

Babies eat everything

There are many studies that look for virtues that could protect against allergic disease, like eating the right food. It could be the case that some healthy, good behavior protects against allergic diseases. But the data from history and poorer countries suggests that what protects most effectively against allergic diseases is not an already recognized virtue. It is something people tend to avoid as soon as they can. Childhood ingestion of dirt ticks all the boxes here. 

During the last year I have spent quite a bit of time wondering about one thing: Why do babies eat everything? Why do they compulsively put everything in their mouths? They do not only taste things after having looked at them carefully. They ambitiously try to reach all things in order to mouth them. I have also noticed that babies seem to be very resilient to infections caused by microbes. My children never seemed to get sick from all the disgusting things they put in their mouths. 

After reading about allergies, I came to think about one possible answer: Babies eat everything in order to train their immune systems for the inevitable. And actually, a research team made up that hypothesis in 2004. These researchers mean that there must be something advantageous in eating everything for babies, otherwise the behavior would have been selected against. The research team assumed that breast milk protected children from some of the danger of the microbes they ingested. But that can't be the case for my children, because I never breastfed. And they ate kind of everything, indoors and outdoors, and never got sick from it (great statistics, I know).

Breastfeeding or not, I think this hypothesis is up to something. Could the rise in allergies in the rich part of the world be due to overzealous parents preventing their babies from eating dirt? This hypothesis both conforms to the income factor, the urban/rural factor and the sibling factor: Rich, urban parents with only one child have both the means and the will to supervise their only child enough to prevent most of the baby-dirt interaction.

Studies indicate that many types of dirt could protect against allergies.Third-world dirt. Karelian dirt. Greenland dirt. Amish dirt. Our immune systems don't seem to be that picky. It most of all seems they need something to tune themselves in against. The Karelia study writes:

"urban people are repeatedly exposed to their own microbiota, which is not enriched by microbes from variable natural environments."

So what if babies get protected against allergic disease when they eat dirt? Any dirt, more of less, as long as it does not derive from humans? Then the question is: Do people stop allowing their babies to mouth things from the ground when they become well-off and have few enough children to keep close watch of the baby? 

A long time ago, when we only had two children, Anders came back from the playground and told me that an unknown woman had informed him that his child was eating sand. He had replied that he was well aware of this but that she could notify him if again if his children were eating cigarette butts. 

The reason why I remember this, except for the fact that I am very good at remembering useless information, is that it indicated that some people really don’t want their children to eat sand. Is that common? It seems no one has found that question important enough for a study. But discussions like this one indicate that parents actually try to prevent their children from putting stuff in their mouths when being outdoors. 

I think the babies-eat-everything theory could maybe also explain why the Hutterites had so many more allergies than the Amish. The study found that the Amish had more healthy, barn-like dust indoors. But it didn't ask how much time babies spent outdoors. I read a book about the Hutterites to find any clues to how much time Hutterite babies spend outdoors, on the ground. The result I found was that the Hutterites might be as good as small mainstream families at keeping their children from eating dirt because of one particular feature: Specialized childcare. Amish mothers work while they take care of small children. Hutterites have systems for childcare, so mothers can work more efficiently when they work. While technically farmers the Hutterites farm in a modern way. The mothers do farmwork while their children are being taken care of by someone else. Meanwhile, the less specialized and more technologically primitive Amish need to take their babies with them when they tend their small-scale kitchen gardens. 

I don't know whether people allowed their children to crawl around and eat a bit of everything during the first half of the 20th century and then successively became more controlling. But I know that people report that they spend at least twice as much time parenting today than people did in the 1960s. This is odd, since many more mothers stayed at home with children in the 1960s compared to now. What are people doing when they parent now that people didn't do in the 1960s? One of those things might be following a crawling baby around, providing the baby with a constant stream of pre-approved CE-labeled toys and thus preventing it from putting anything unauthorized in its mouth.

Let baby crawl outdoors

The hygiene hypothesis has one very pleasant feature: it turns the idea of virtue and vice upside down. The mother who complained that our baby ate sand probably thought she was promoting public health. Maybe she was doing the opposite.

Sooner or later, researchers will probably find out which microorganisms protect us from atopic disease and pharmaceutical companies will make drugs containing those microorganisms. Then ambitious parents will have one more chore to add to their long list. When they are done following their babies around and distracting them from the real world with appropriate toys, they will have to find time to give their babies their daily drops of allergen protection microbes. But until then, rich, urban and ambitious parents might want to copy a thing or two from us lazy and careless parents and let their babies crawl outdoors, savoring the full taste of the real world.

Edit: After having discussed this theory with people on Astral Codex Ten, I have learned another thing: Peanut allergy is unusual in Israel because a very baby-friendly peanut snack is very common there. People feed their babies those snacks and those babies get much less allergic than Jews in other places. An article in Nature about that phenomenon explains that it seems to matter how a child gets into contact with a food allergen: Eating it is protective, while inhalation and skin contact seems harmful. And who knows this principle is limited to food allergens? Maybe eating all allergens is protective, including pollens and mold and cat sweat. Another reason to allow babies to eat (almost) everything they like.