One key to a healthy immune system, a lower rate of allergies and a better mood might be getting dirty. But not just any dirt. This isn’t the dust in your house or grease from the garage. The dirt I’m talking about is in the garden, or your pots if you live in an apartment.
According to the Asthma and Allergy Foundation of America,1 roughly 1 in 3 adults and 1 in 4 children in the U.S. have seasonal allergies, eczema or a food allergy. In 2021, 81 million people were diagnosed with seasonal allergic rhinitis, which was 26% of adults and 19% of children. Seasonal allergies cause 3.1 million missed workdays and cost $8 billion annually.2 In other words, it’s nothing to sneeze at.
Your gut microbiome, which is affected by your exposure to dirt, also influences your mood, including depression and anxiety. There is a crucial relationship between anxiety and depression.3 In 2020 and 2021, researchers estimated the prevalence of anxiety from 26.9% to 31.9% and the prevalence of depression from 28% to 33.7%.4 Those percentages represent a large part of the U.S. population.
The first line of treatments for seasonal allergies, anxiety and depression are medications, many of which come with a long line of side effects. The good news? There is strong data to suggest that by carefully cultivating your gut microbiome you may influence your risk and severity of allergies and mood disorders.
Why a Little Bit of Dirt May Be Healthy for You
It’s called the Farm Effect or the Hygiene Hypothesis. The basic idea is that the more you're exposed to soil and dirt, the more diverse your gut microbiome and the stronger your immune system, which affects many physiological processes.
In 1989, David Strachan a professor of epidemiology at the University of London/St George's Hospital5 published a paper6 proposing that children who were exposed to more germs were less susceptible to developing disease and illness as they grow. He found differences between children who had more and fewer siblings. This was dubbed the "Hygiene Hypothesis," which was then framed as "the Old Friends" or "microbiota hypothesis."7
A 2012 paper8 found that microbial diversity plays a central role in protective effects against asthma and allergies. The researchers found individuals exposed to cows, straw and drinking unprocessed, raw milk just three times experienced protective effects from asthma but not atopy (eczema and allergic rhinitis).
This was dubbed the "Farm Effect," "one of the most compelling observations to arise from investigations of the microbiome in asthma development, and it is one of the key phenomena that has maintained the relevance of the hygiene hypothesis."9
Exposure to microbes when you're young can lead to a much lower risk of asthma and allergic inflammation when you're older. Researchers have proposed exposure to animal-associated microbes is key, yet analysis of the published data finds potential gaps and questions the specific exposures that offer the best protective effect.
A 2016 study10 in The New England Journal of Medicine identified some significant differences. The researchers analyzed the rates of asthma and allergies among Amish communities,11 including the Hutterites, who are a group living largely in Canada and the northwest U.S. While both communities make their livelihood from farming, Amish families use traditional methods, including livestock power tools while Hutterites use modern farm machinery.
The researchers found that only 10% of Amish school children were diagnosed with asthma and allergies while up to 30% of Hutterite children experienced those conditions. The researchers concluded that the dust from the farm fields might protect the Amish children while being sheltered from the exposure might increase the vulnerability of Hutterite children.
Proper Hygiene Has Its Place
Regular hand washing became a strong focus of public health agencies during and after 2020 to remove germs, avoid illness and prevent the spread of germs to others.12 The importance of hand washing to prevent the spread of infection became a worldwide focus in 2008 during the first Global Hand Washing Day.13
Many parents spend a good deal of time teaching young children the importance of taking baths, washing their hands before meals or staying as clean and germ-free as possible. Is this counterintuitive to the Farm Effect, Hygiene Hypothesis and multiple studies demonstrating that many of our kids may have become too clean for their own good?
No, it isn’t. Exposure to common viruses is not what seeds your gut microbiome with beneficial bacteria. Hand washing to reduce the spread of viral infections is necessary, but digging into a handful of soil or hiking through the woods offers exposure to different live cultures.
Being Out in Nature Helps Seed Your Microbiome
Someday, today's population might be known as the indoor generation. A report on a survey from window manufacturing company VELUX found nearly 1 in 4 Americans spend their entire day indoors without ever going outside.14
On average, the 16,000 people from 14 countries who were surveyed believed they spent 18% of their day inside, but the actual amount was 90%. Peter Foldbjerg, head of daylight energy and indoor climate at VELUX, said in a press release:
"With the pressures of modern life, we are all now firmly a part of the Indoor Generation and we need to understand the implications on our health and wellbeing of life indoors, as well as outdoors, when it comes to polluted air.
We are a 24/7 society and this has disconnected us from the natural rhythms of nature — our circadian rhythm, a neurophysiological term for the 24-hour body clock that anticipates and adapts our physiology to the different phases of the day, sleep and wake cycle. All of this impacts our sleep quality and general health."
So, while the first step is to step outside, the second step might be to get your hands in the dirt. Scientists have discovered the broad range of benefits that microbes play on mental and physical health. Christopher Lowry, professor of integrative physiology at the University of Boulder Colorado told The New York Times that when we are outside, "we’re breathing in a tremendous amount of microbial diversity."15
A study from Finland revealed that children who went to nature-oriented daycare centers experienced greater biodiversity in their skin microbiome and gut bacterial community. The researchers found correlations between the gut microbiota and their immunological systems concluding that the results:16
"… support the biodiversity hypothesis and the concept that low biodiversity in the modern living environment may lead to an uneducated immune system and consequently increase the prevalence of immune-mediated diseases."
Anti-inflammatory Fat in Soil-Dwelling Bacterium May Affect Mood
Soil exposure may not only help allergies and asthma, but it could affect your mood. In a 2004 paper17 published in the Annals of Oncology, physicians reported the effect of injecting SRL172, (killed Mycobacterium vaccae) alongside chemotherapy to treat non-small cell lung cancer.
The researchers had hypothesized this may help the body fight cancer based on previous studies where the suspension was used in individuals with drug-resistant pulmonary tuberculosis18 and to boost immune system response.19
However, the data showed there was no difference between the control group who did not receive SRL172 and the intervention group in overall survival, which was the primary endpoint of the study.
The researchers found that patients who received SRL172 experienced improved quality of life in the time they had left. This was a unique demonstration of the influence the bacterium had over mood in a group of individuals who were facing a challenging health condition.
In 2007,20 Lowry injected heat-killed or M. vaccae into mice and exposed them to stress tests. The animals that received the bacteria demonstrated less stress during the tests. A later research group21 fed mice the bacterium and found they ran mazes twice as fast and enjoyed doing it. The researchers theorized it had something to do with the effect on the immune system.
In 2010, Dorothy Matthews of the Sage Colleges, presented her results at the annual American Society for Microbiology meeting. They found the bacteria appeared to stimulate the hippocampus, which is responsible for spatial memory and changed the mice's mood as they demonstrated less anxiety-related behavior.
"It just shows that we evolved with dirt as hunter-gatherers," she said. "So, turn off your TV and go work in your garden, or walk in the woods."22
Lowry continued studying Mycobacterium vaccae and in 2019 he published information on anti-inflammatory fat found in the bacterium that might explain the effect it has on mood and stress.23 The anti-inflammatory fat — 10(Z)-hexadecenoic acid — appear to inhibit inflammation in immune cells. The research supports the Farm Effect and brings researchers closer identifying how it could help reduce stress and anxiety for those in high-stress jobs.
Embracing the Outdoors May Reduce Your Seasonal Allergy Reactions
Thankfully, you don’t have to live on a farm to experience the Farm Effect. While taking probiotics and prebiotics can help reseed your gut microbiome and affect your overall health, several more steps can prevent damage and help improve your microbiome diversity.
Stop using antibacterial soap and detergents — Regular soap and water can clean your hands, and there is no evidence that antibacterial soap offers more benefits.24 |
Clean up your diet — Choose organically grown foods and eliminate products grown with genetically modified seeds or sprayed with pesticides and insecticides as these destroy your gut bacteria. |
Eat fermented foods — Fermented vegetables are inexpensive and easy to make at home and provide a host of health benefits, including seeding your gut microbiome. |
Go gardening — No matter where you live you can garden. Even in an apartment, you can grow plants in pots and get your hands dirty. Just remember to leave the gardening gloves for when you’re pruning plants with thorns and use your bare hands for planting. |
Get dirty — Children love getting dirty, and adults may want to take a page from their playbook. Think about playing in the dirt or mud, making mud pies, bug hotels, fairy gardens or even mud art. Take up a mud sport like mud runs, mountain biking or hiking. The idea is to just get dirty. "I think we underestimate how much exposure we get from simply being outside," Lowry said.25 |
Not all dirt is good dirt — Steer clear of dirt in polluted areas that contain harmful contaminants and can be unhealthy for children and adults. Don’t use chemical weed killer or glyphosate and choose the best soil possible for your pots and raised gardens so you enjoy the same benefits as your plants. |