You may have noticed that in your circle, children who grew up in the countryside, and especially on a farm, seem less prone to allergies than their city-dwelling cousins. This is not an impression, it is a well-documented statistical reality. But why? L’air of the countryside would it be purer? Do farm children have special genes? The answer, as is often the case in immunology, is more subtle and much more fascinating.
A solid scientific observation: the studies that changed our outlook
For several decades, industrialized countries have witnessed a spectacular increase in allergic diseases: asthma, eczema, rhinitis and food allergies now affect nearly one in three children in certain urban regions. However, this phenomenon is not uniform. In the early 2000s, researchers began to note a troubling statistical anomaly: children living on farms seemed spared from this epidemic.
The European study PARSIFAL, published in 2006, marked a turning point. Comparing thousands of children aged 5 to 13 from farms, rural non-farm areas and urban areas, researchers observed a striking difference: farm children had significantly less asthma, eczema and rhinitis allergic than their urban peers. This was not an effect of rurality per se, because children living in the countryside without contact with the farm did not benefit from the same protection.
A few years later, the GABRIELA study (2010) confirmed and refined these results by focusing on more than 8,000 children in five European countries. His conclusions were clear, the earlier the exposure to the farm environment, ideally from the first year of life, and the more diversified it is (contact with cowspigs, chickens, hay and straw), the stronger the immunological protection. The figures speak for themselves, according to this work, children who grew up on a farm see their risk of developing asthma, eczema or allergic rhinitis reduced by 50 to 80% compared to urban children.
A question then urgently emerged: what biological mechanism can explain such a considerable difference?
The theory of hygiene: when too much cleanliness weakens immunity
To understand what protects farm children, we must first understand what makes urban children vulnerable. This is where what scientists call the hygiene theory comes in, proposed in the 1980s by British epidemiologist David Strachan.
The idea, counterintuitive at first glance, is that our immune system has evolved over millennia in an environment constantly populated by microorganismslike the bactéries from the ground, the parasites or the virus varied. To function correctly, it needs, from the first months of life, to be “confronted” with this microbial diversity. It is through this contact that he learns to distinguish dangerous attackers from harmless substances.
In our hyper-controlled urban environments, this stimulation is lacking. THE immune systemfor lack of real enemies to fight, can then turn against innocuous targets: pollens, mites, food proteins, or even its own tissues in the case of autoimmune diseases. This is what I like to explain to parents by comparing the immune system to an army: an army that has never seen combat, that has never been trained to distinguish enemy from ally, will tend to shoot at everything that moves.
The farm environment, conversely, offers a true “immune training camp”. It is exceptionally rich in various microbes, bacteria and mushroomscoming from animals, soil, hay and straw. These microorganisms naturally colonize the microbiota of the child, that is to say all the bacteria which live on his skin, in his respiratory tract and, above all, in his intestine.
However, the microbiota is much more than a simple passenger. It is a central player in immune education. A rich and diverse microbiota “teaches” immune cells to modulate their responses, not to get carried away by innocuous stimuli. Conversely, a poor and undiversified microbiota, which is typically observed in urban children exposed to excessive hygiene, leaves the immune system naive and hyper-reactive.
Among the molecules protective barriers identified on farms, endotoxines occupy a special place. These compounds present on the wall of certain bacteria, abundant in stables and fodder stocks, have demonstrated in multiple studies a protective effect against the development of asthma and allergies. They act as alarm signals which, paradoxically, calm theinflammation in the long term by conditioning the immune system not to overreact.
What researchers today call the firm effect is therefore the sum of these early, diversified and continuous exposures, a “microbial bath” which programs the immune system for a balanced and measured response.
What can city dwellers learn from this phenomenon?
Of course, there is no question of transforming your city apartment into a stable. But researchers have identified several factors that parents living in cities can put into practice to promote the immune development of their children.
- Having a pet from a young age: this factor is among the best-supported recommendations. Several studies show that children who grow up with chienand to a lesser extent a cat, present a reduced risk of allergies. Dogs, in particular, act as vectors for external microbes: they bring bacteria from soil, grass and the external environment into the house, thus enriching the domestic microbiota.
- Spending time in nature: regular outings in the forest, playing in the grass, contact with garden soil expose the child to a microbial diversity much greater than that of urban interiors. Let your children touch the earth, build cabins, climb trees : each handful of soil contains billions of bacteria, and their immune systems benefit from it.
- Limit excess disinfection: the systematic use of antibacterial products, such as gels hydroalcoholic or disinfectant wipes, deprive the child of beneficial microbial contacts. This doesn’t mean giving up hand washing after going to the toilet or before preparing food, but accepting that a little “dirty” doesn’t hurt. THE nez collé à la window the bus? Maybe not. But hands in the garden soil? Absolutely.
- Take care of your diet: a diet rich in fiber (vegetables, fruits, légumineuses) nourishes the intestinal microbiota. Fiber is the preferred fuel for good bacteria, which in return produce beneficial molecules for immune regulation.
- Favor vaginal birth andbreastfeedingÂ: these two factors are partly beyond the control of parents but have a documented impact. Vaginal birth exposes the child to his mother’s vaginal microbiota, colonizing his intestine with protective bacteria. Children born by césarienne have a different initial microbiota, but this difference can be attenué through breastfeeding. THE breast milkin fact, contains prebiotics which selectively promote the development of good bacteria in infants.
A word of caution is in order, however: the firm effect is a statistical phenomenon. Many city children will never have allergies, and some farm children will develop them. There génétique plays an important role, as do other environmental factors that we do not yet control. The objective is not to eliminate all allergies, that would be unrealistic, but to understand the factors that influence them to give each child the best chance.
