No sooner is the cold season drawing to a close than more and more Brits are immediately gearing up for a battle against another invisible foe: pollen. In GB alone, millions of people suffer from itchy eyes, a blocked nose, sneezing fits, exhaustion and, in some cases, even asthma-like symptoms – and the trend is rising!

Alongside antihistamines and symptom-specific treatments such as nasal sprays or eye drops, more and more sufferers are looking for alternative solutions – and in doing so are coming across an approach that suggests a link to a surprising organ: the gut!

To understand this surprising connection, it is necessary to take a closer look at the processes taking place in our body as it battles against pollen and grasses.

In short, an allergy is a malfunction or overreaction of the immune system. It mistakenly interprets harmless substances, such as microscopic pollen, as a potential threat and switches to defence mode. This triggers a strong immediate reaction. In the process, the immune system releases a substance produced by the body called histamine, which ultimately manifests itself in the typical allergy symptoms.

But the question arises: what role does the gut play in this?

To answer this question, we need to look back over 30 years. At that time, it had already been noted with concern that the proportion of people with allergies in the general population was continuing to rise. The theory presented in 1989 by a professor named David Strachan caused a correspondingly large stir – not least because of its rather paradoxical-seeming basic premise:

He posited that improved hygiene conditions were responsible for the rising number of allergy sufferers. According to this theory, children are coming into contact with germs less and less frequently and experiencing fewer infections, to which the immune system reacts with allergies – in short: children are now too healthy and are consequently developing allergies.

So is the answer to the question of how allergies can be curbed ‘more illnesses’? Is humanity stuck between a rock and a hard place?

In the search for answers, a series of further studies investigated the link between exposure to bacteria and the development of allergies. And lo and behold: Strachan’s hygiene hypothesis initially appeared to be borne out.

It was found that children born by caesarean section have a fivefold higher risk of developing allergies later in life compared to children born vaginally. Here too, the explanation is attributed to bacteria: during a vaginal birth, a baby comes into contact with various bacteria in the birth canal, whereas with a caesarean section, it moves from the ‘germ-free’ womb directly into a delivery room that is also more or less germ-free; contact with bacteria: none.

A similar picture emerged from the Europe-wide GABRIEL study. It showed that farm children, who naturally come into contact with a wide variety of bacteria more often, are far less likely to suffer from hay fever or allergic rhinitis than city children.

So has Strachan, with his theory, managed to crack the allergy code?

Although Strachan’s idea provides an important foundation for further research, more precise connections were only discovered years later – such as the vital role played by the gut microbiome in this context.

The gut microbiome refers to the totality of living microorganisms (mainly bacteria) in the gut. They form a complex ecosystem, similar to a tropical rainforest. It, too, can only thrive if all the organisms living within it are in harmony with one another.

If, for example, one plant species becomes overgrown, this can disrupt the entire balance. These factors can also be applied to the gut microbiome, which, according to current research, consists of up to 100 trillion bacteria! The bacteria can be divided into different strains – just as the plant species in the example above each have different characteristics and functions.

Unfavourable external influences, such as an unbalanced diet, stress or certain medications, can lead to some bacterial strains becoming more prevalent, thereby suppressing others or even causing the total number of gut bacteria to decline.

The resulting imbalance is scientifically referred to as dysbiosis.

According to studies, such dysbiosis has so far been linked to symptoms such as fatigue, obesity and a compromised immune system – and possibly also to allergies? Could the lower prevalence of allergies among children born naturally or raised on a farm be due to their gut microbiome developing more effectively as a result of contact with bacteria?

Allergists – and those affected – had to wait quite some time for an answer to this question. Scientists took a first major step with the launch of the American Gut Project in 2012: technical advances had simplified and reduced the cost of whole-genome sequencing, meaning that, for the first time, a large volume of data on the gut microbiome could be collected and analysed.

This revealed that the microbiome of people with allergies differed significantly from that of unaffected individuals: not only did it contain a lower number of bacteria, but diversity was also markedly reduced. This closed the gap in Strachan’s hypothesis and demonstrated that the microbiome and allergies were indeed linked. The question of ‘whether’ had thus been answered – but the question of ‘how?’ continued to occupy researchers.

In 2020, a Japanese researcher named Shimon Sakaguchi finally made a breakthrough: he discovered what are known as regulatory T cells. These cells ensure that the immune system responds appropriately to certain substances; in other words, they are responsible for ensuring that the immune system reacts differently to a potential threat – such as a virus – than to a harmless substance – such as pollen.

But what does this have to do with the gut? Quite simply, these special cells are produced in the gut. However, if dysbiosis is present, it negatively affects the production of T cells, while a lack thereof can in turn promote allergic reactions.

To support this hypothesis, scientists conducted an experiment on mice: a group of so-called ‘germ-free mice’ – mice that had been isolated from germs since birth – were given the microbiome of allergy sufferers. The result: these mice also showed signs of allergies. Even more impressive was the reversal of this experiment: the now-allergic mice were subsequently given the microbiome of non-allergic mice. The result: the allergies disappeared. The link between the gut microbiome and allergies was thus clearly demonstrated!

In light of this groundbreaking discovery, the question now arises: how could these findings be used to help people with allergies – including humans? Should the microbiome of their non-allergic peers also be transferred to them? And how can a microbiome be transferred in the first place?

In principle, transferring one person’s microbiome to another is entirely possible – and has, in fact, been practised for over 1,000 years. As far back as 4th-century China, doctors administered the microbiome of healthy individuals to patients – via the oral administration of human faeces!

Although this procedure has been improved over the last millennium – nowadays, so-called faecal transplantation is carried out either via a tube directly into the small intestine or by taking capsules – it can hardly be described as a pleasant treatment. Furthermore, such treatment is not only very expensive but also associated with various health risks. For these reasons, it is only the treatment of choice in very exceptional cases.

But what if there were a way to help allergy sufferers achieve a balanced microbiome by other means – a way that, as far as possible, avoids human faeces, tubes, risks and excessive costs?

This is precisely the approach taken by so-called probiotics, i.e. preparations containing live micro-cultures that colonise the gut and are thus intended to correct dysbiosis. Currently, these pills and powders are experiencing a veritable hype on social media and elsewhere, making a name for themselves through aggressive advertising, sky-high promises and unbeatable special offers.

Without prior knowledge, it is almost impossible to separate the wheat from the chaff. For this reason, the SYNformulas team of experts has taken a close look at five products and assessed them using objective, scientific criteria.