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Immune system calibration: avoid allergy, asthma and autoimmune conditions (the ‘old friends’ hypothesis)

References / Further Reading:

Old friends hypothesis: 

Gut microbiome / immune system interaction:

Farming and childhood allergies:

Raw milk protective against allergies:

Pet ownership: 

Indoor living and allergy:

Variability of bacteria in the home: 


Breast milk microbiome

Endocrine Disruptors and the immune system:

Infant mouthing and immunocalibration:


Immune system calibration: avoid allergy, asthma and autoimmune conditions (the ‘old friends’ hypothesis)

It seems like our immune systems have gone haywire in the last few decades. Rates of asthma, eczema, allergies and autoimmune conditions have got completely out of hand. It’s very strange that modern society appears to accept all this as normal, rather than taking immediate action. Some of these are serious medical conditions affecting young kids, which were virtually unheard of just a couple of generations ago. Meanwhile loads of the population struggle to fight off mild infections.

And there is a simple explanation for all this, but you’re certainly not going to hear it from any health service. Modern health care is attempting to manage the symptoms with drugs rather than looking into the root causes. And in this case, modern health care is one of the factors actually driving some of these problems. Rates of these conditions are only going to increase, so the sooner you know about this the better, particularly if you have young children or grandchildren, or are planning to get pregnant.

The key concept here is something called the ‘old friends’ hypothesis.

The ‘old friends' hypothesis suggests that for our immune systems to be calibrated correctly, we need adequate exposure to certain beneficial micro-organisms. If your immune system is correctly calibrated, it should be efficient at dealing with harmful bugs that cause infection, rather than reacting to allergens or attacking your own body. The beneficial micro-organisms that we need exposure to include bacteria from various microbiomes (a microbiome being a community of micro-organisms living together). Beneficial bugs have been helping to calibrate human immune systems since our hunter gatherer days, hence we can refer to them as ‘old friends’.

'Old friends’ originate from a number of different microbiomes, which we can divide up, into those that come from our mothers, and those found in nature. We can imagine this through the lens of our hunter gatherer ancestors.

Firstly, during birth, a baby is exposed to the mothers vaginal microbiome as they come down the birth canal, as well as to bacteria from the perineum which will include bacteria from the mother’s bowel. These are probably the first micro-organisms to cover the newborn baby and get into the baby’s gut, starting the formation of the newborn gut microbiome. Next, breast milk during the first few years of life not only provides important prebiotics to support the developing gut microbiome, but also has a microbiome of it’s own, the human milk microbiome, adding more bugs into the mix. As a hunter gatherer, you would be interacting with beneficial microorganisms, including bacteria, within your environment on a daily basis from day one. These would include the bugs in soil and on plants, and the bacteria on hunted animals carried back to camp.

When you are exposed to ‘old friends’ from any of these microbiomes, they get on your skin and may become part of your skin microbiome. Some also inevitably get ingested and end up in your gut, where they can either interact with, or become incorporated into, your gut microbiome. The gut microbiome provides a key interface between the outside world and your immune system, and plays an important role in educating your immune system as to what is friend and what is foe. This is most important during infancy, when the immune system is first being programmed.

In the modern world, our relationship with these ‘old friends’ has taken a major hit. If you agree with the ‘old friend’s’ hypothesis, you can probably figure out why modern living has the potential to cause such a problem for our immune systems. Anything that severs our connection with old friends in any of these microbiomes, has the potential to increase our risk of diseases caused by faulty immune calibration.

C-sections disrupt the initial development of the newborns gut microbiome, with bugs from hospitals and hospital staff skin likely to be the first bugs encountered. We want a baby’s gut microbiome to be formed with ‘old friends’ from Mum, not from micro-organisms found in hospitals, which are most certainly not our friends. The modern world has also seen a massive reduction in breast feeding rates and duration. Traditional rural farming lifestyles have been replaced with city living. The more humans cram together, the more old friends get replaced with bugs that cause infection. Interaction with soil and animals have hugely reduced, and people have increasingly indoor lifestyles, devoid of interaction with ‘old friends'. And often when people do go and finally interact with these microbiomes in nature, they come home and wash their hands in an attempt to kill any bugs they may have encountered.

The result of all this is that our skin microbiomes, our gut microbiomes, and our immune system calibration have all taken a major hit.

This is why being brought up on a farm with livestock is known to reduce your risk of developing allergies and asthma. Lots of old friends about. An important caveat is that this is small scale traditional non-intensive animal farming.

Interestingly, as well as exposure to old friends from animals, plants and soil, it’s thought that the consumption of raw unpasteurised milk, common amongst children growing up in a traditional farm setting, is also an important factor. Unpasteurised milk contains probiotics, beneficial bugs that can support your gut microbiome. Pasteurisation represents a type of processing that can kill these probiotics, and therefore reduce the potential health benefits of milk.

Pets are also good at dragging old friends back in to your house, and the sort of lifestyle choices you make will impact what sort of micro-organisms you have at home.   

I’ve put lots of further reading and references in the description, so now I’ll just go on to what actions we take as a family based on this information. Disclaimer: These are not general recommendations, what you choose to do will be based on your own circumstances, opinions and perception of risk.

Daily actions 1: Maximise interaction with old friends in nature.

We try to maximise time outdoors, aiming for daily contact with trees, plants, animals and soil. Ideally the outdoor setting should be as wild as possible, but the garden is fine as well. When it’s warm and sunny we’ll make sure we have plenty of skin exposed in order to maximise vitamin D generation.

Daily actions 2: Avoid products that damage old friends.

We try to avoid chemical cleaning products, and harsh or toxin filled personal care products. They are all bad for the environment, harmful to ‘old friends’ and damaging to gut and skin microbiomes. Modern soaps can also strip your skin’s natural barrier allowing a direct route for potential allergens straight through your skin into your blood stream. They can also give you dry skin and contribute to eczema.

If I feel the need to use soap (which, when I’m not at work, is not very often at all), then I use a bar like this one, which has in it only olive oil, water and salt, and comes packaged in cardboard. Soap in a plastic dispenser does not have a place in my house. My kids don’t routinely wash their hands before meal time.

Daily actions 3: Support the gut microbiome

If you do everything right with old friends but directly damage your gut microbiome, you can undo all your hard work, so we try to have a diet that supports the health of our gut microbiome. That means avoiding overly processed modern foods or artificial chemical ingredients, and consuming a whole foods diet with plenty of fibre. We also enjoy fermented foods such as sauerkraut and kefir, and when possible, raw unpasteurised milk. High quality fatty animal products provide very important vitamins and minerals for optimal immune function, so we always eat plenty of these, see the video on animal fat linked in the description for that topic. We avoid non-organic food, since pesticides like glyphosate not only wreck soil and plant microbiomes, but the residue on-non organic foods can damage your gut microbiome too. I’ve put links in the description if you want the full run down on both healthy eating, and glyphosate. And of course antibiotics should be avoided as much as possible since they can cause major damage to your gut microbiome.

Daily actions 4: Avoid other factors that disrupt immune calibration.

Finally, we avoid other things that can disrupt immune calibration. Poor sleep and stress are very quick ways to cause disruption, so these are something we are always working on. It’s not uncommon that the onset or worsening of autoimmune conditions can be correlated to stressful times in life. And finally, all the toxic chemicals, pollutants and plastics that humans are now surrounded by, as well as being endocrine disruptors that mess with your hormone systems, are directly toxic to your immune system, so we avoid these as much as we are able, video on endocrine disruptors will be linked in the description.

And of course we should always encourage breast feeding, but also child birth in the most healthy environment which is in your own home, rather than in hospital.

Dr Philip Bosanquet

The Low-Tech Lifestyle Medic


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