As dusk falls in the Finnish city of Lahti on a still cool day in May 2016, a crew of workers ran into the yard of an empty children’s center. Under the swings and gyms in the jungle, they set up squares with forest floors – soiled bushes, shrubby strawberry bushes, slimy meadow grasses and velvety mounds of moss – gathered from the forest somewhere in the less developed part of the country. They put a soft green sod around the edges. In the morning, when the children arrived, they discovered their playground – a former expensive perfume made of asphalt, gravel and sand – turned into micro-oases of the desert overnight.
This scenario takes place three more times this month in kindergartens in Lahti and 500 miles west in the town of Tampere. This was not the work of some nature-loving guerrilla artists, but the beginning of an ambitious scientific experiment to see if the lack of microbes in the urban environment could turn people̵
You are probably more familiar with the “hygiene hypothesis”. First described by a British epidemiologist named David Strachan in the early 1990s, he argued that the rise in chronic disorders associated with an overactive immune system – such as asthma, diabetes and allergies – was caused by children growing up in -sterile blisters. Immune systems are the most basic objective classifiers. Their job is to recognize what I am and what else. The microbes encountered at the beginning of life are the first teachers in this process – they help the developing immune system to decipher what is dangerous and what is not. The more families used antibacterial soaps and gels, locked themselves in tall apartments, and drove cars through concrete jungles, the less habitat there was for bacteria, protozoa, fungi, and viruses to thrive – and less likely to be a developing child. immune system to deal with them. And less exposure means fewer training opportunities. A poorly trained immune system can fail when it’s time to differentiate between the body’s own cells and food allergens, or intestinal microbes, or pollen in the air.
Laboratory experiments with rodents in the early 2000s supported this idea: wild rats had a well-tuned immune system to fight dangerous pathogens, but no small irritants, while their lab counterparts overdid the slightest stimulus. Human epidemiological studies have also provided circumstantial evidence that the incidence of allergies and asthma is higher in more industrialized areas than in rural areas. To counteract these supposed negative effects of the urban, modern lifestyle, dozens of companies have sprung up to boost immune-boosting probiotics – pills and drinks and creams filled with cocktails of live bacterial cultures. In the Covid-19 era, thousands of posts labeled #immuneboost were posted on Instagram every week, promoting these and other home remedies. So far, there is little evidence that any of them worked.
That is why in recent years, scientists like Sinkonen have taken this idea one step further. People are increasingly living in deserts with microbiodiversity, they observe, skipping the exposure to various harmless mistakes. “The immune system does not recognize microbes by species, but by species,” says Sinkonen. “Probiotics usually contain only one or two types of bacteria, so they are unlikely to activate the entire immune system. We wanted to see what would happen if we imported a whole diverse microbial environment. “Therefore, forest floors in playgrounds – the first randomized controlled trial to test the hypothesis of biodiversity in children. Biohacking, but make it cute.