While we can’t say for sure why allergy rates are increasing (and it’s unlikely down to one factor alone). There are some things that we do know. Allergies tend to run in families, so we know genetics are one culprit. This genetic risk factor is known as atopy. This means that children, where one or both parents have an allergic disease, are much more likely to develop these conditions (1). The ‘atopic march’ is a term used to describe a genetically predisposed individual’s progress from one type of allergy to another, with age. For example eczema at birth, then food allergy and then asthma. However, just because your child has eczema doesn’t mean they’ll get more allergies. It just means there’s a higher risk of it happening (2). But genetics is only part of the picture since we have been carrying similar genes in our DNA for thousands of years without being allergic.
In fact, allergies are increasingly considered to be a by-product of our modern lifestyles, more likely to affect people who are distanced from traditional upbringings (3). At least part of the answer lies in changes to the composition of your body’s good bacteria — collectively known as the microbiota — the majority of which live in our guts. With modern-day dietary and lifestyle changes, antibiotics, pollution, our own inner biodiversity is being slowly eroded, and with it our immunity.
Microbes & immunity – friend or foe?
A large part of what our immune system does is fight off germs to keep us well. But our understanding is actually much broader: Immunity ensures we respond appropriately when we encounter anything in the world around us — not only harmful germs. With the vast improvements in sanitation and healthcare, germs are no longer the enemy in our modern-day lifestyles. In fact, 99% of germs that surround us at any given moment (and we are surrounded everywhere all the time) do not cause disease. Rather, they are healthy ‘good’ bacteria — our microscopic health allies and immune system educators. Your immune system is all the time being calibrated by your body’s good bacteria to only respond to things that are actually threatening. Our relationship with ‘good’ microbes on us, in us and around means we are actually super ecosystems. But if that system breaks down it can lead to immune-mediated diseases such as allergy.
Time to abandon the hygiene hypothesis
Decreased exposure to infections in early life through improved ‘hygiene’ was originally thought to increase the risk of allergy. The idea that there might be a link between the rise in allergy and a decline in infection, known as the ‘hygiene hypothesis’, was proposed back in 1989 (4). Early childhood exposure to germs was thought to protect from allergy by encouraging proper immune development. But are allergies really the price we pay for freedom from the burden of killer infections that our grandparents feared yet are rare in our modern world?
True, proper development of our immune system is supported by interactions with germs but hygiene is a misnomer. The hygiene hypothesis has now been largely been overthrown, replaced by the ‘Old Friends’ Hypothesis (5). This suggests that rather than being too clean, the most important change in our environment that leaves us open to allergies the loss of contact with our ‘old friends’ – the many harmless microbes in us, on us and around us from birth.
Interacting with these ‘old friends’, are not the exposures to colds, flu or serious childhood diseases, but rather the 99% of harmless microbes in our environment. Our immune systems need to ‘see’ these good germs which in turn provide vital inputs that educate and shape our immunity from birth. This process serves to diversify our own flourishing microbial ecosystems which are in charge of training and shaping our immune systems, tinkering with how our immune system chooses to respond or ‘tolerate’ harmless things in our environment. Much of this happens in the microbes’ own backyard – our guts! In fact, these days, there is little doubt that your gut resident microbes, have a big say in how your whole immune system develops, including how whether you develop allergies or not (6).
So it follows that if your gut microbiota are in charge of training the immune system. When there are alterations in the composition of our gut microbiota, consequences like allergies might arise. But how? The gut microbiota is a changing ecosystem, containing trillions of bacteria, continuously shaped by many factors, such as dietary habits, seasonality, lifestyle, stress, antibiotics use, or diseases.
Here are some of the key factors affecting this relationship between microbes and health?
1. Us humans are diverse ecosystems, and so are our environments.
Our environment is becoming rapidly urbanized with these drastic changes interrupting the healthy development of our ‘old friends’: dirt is good (7). Disconnection from nature is not. For example, soil has a microbiome and it’s where we used to get many of our good bacteria from. Acquiring soil and other harmless environmental microbes such as those of fresh produce that we eat are called ‘horizontal transmission’. Even the air we breathe carries its own microbiome (8). Today, we are so far removed from these natural environments, that we’re missing out on some of the crucial microorganisms that used to populate our own microbiome. Now I am not suggesting we all start eating dirt (there are definitely risks there), but gentle exposure to germs that live in natural environments. Getting outdoors into parks and, where possible, the countryside, particularly during childhood.
2. Early life influences
including C-sections and formula feeding alter gut bacterial species (gut more info here) (9, 10,11). But these are not always within our control. Plus its complex, just having a c-section and formula feeding isn’t necessarily a shortcut to your kid developing allergies.
3. Changing dietary habits
Just like us, bacteria in our guts need to eat. When your microbes chow down on fiber-rich diets, they produce a veritable banquet of metabolic trash by-products known as ‘postbiotics’ that are key in educating our immune system. Turns out we are now eating much less fibre than ever before, replacing it with fibre poor processed food with its potentially microbiome-harming high levels of salt, sugar, and fat. Plus sweeteners, additives, emulsifiers are changing our microbiomes in ways that are only just beginning to be explored (12).
4. The changing way our food is produced
Where and how it’s grown, what it was sprayed with and how far it has travelled) influences the number and variety of the microorganisms. Eating produce grown in healthy soils, typically associated with organic cultivation, which has a significantly more diverse bacteria population than their conventionally grown counterparts (13).
5. Use of antibiotics and medications
A study of children who were given antibiotics before the age of two showed that a startling 74 percent of them were, on average, nearly twice as likely to have developed asthma by the time they were eight. The more courses of antibiotics kids received, the more likely they were to develop asthma, eczema and hay fever even if they did not have a genetic risk (14).
The future is bright
While we have treatments for the symptoms of allergy, we do not yet have a cure or the ability to prevent them from developing in the first place. The good news is that increasing awareness in both patients and healthcare providers means that although allergies are on the rise, serious complications and fatalities are not. But there remains much work to be done in preventing the development of allergies in the first place. Thanks to a century of germaphobia and hyper-sanitation, industrialisation of food and overuse of antibiotics, we’ve inadvertently caused a mass extinction of microbes inside us sending our immunity haywire and allergies through the roof. The environmental inputs your immune system needs to develop properly are complex, and not fully understood. Even if you are doing everything right, the modern world in which we live is perhaps now lacking many of the key microbial inputs our immunity needs. The good news is that our improved understanding of these ‘old microbial friends’ is taking us leaps and jumps into future treatments and early protection from allergies.
About the author
Immunologist Dr. Jenna Macciochi unravels the science underlying strong immunity and teaches us how to be well in a modern world. Currently a lecturer at the University of Sussex, she specialises in understanding how nutrition, lifestyle, and gut health interact with the immune system in health and disease. Jenna is a Brighton (UK) based mum to twins, a perpetual kitchen experimenter with a passion for movement and exercise.
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