That time of year is almost upon us, when millions of people in the UK succumb to pollen-induced sneezes, sniffles and itchy eyes: the dreaded hay fever.
Now scientists may have identified a key reason why so many of us suffer allergic symptoms, but many others do not. Research by the University of Porto in Portugal has found that people with hay fever have different fungus in their noses.
We all have a community of fungi in our noses, the nasal mycobiome, which forms part of the nasal microbiome, that also includes bacteria and viruses that live there.
But people with hay fever – or seasonal allergic rhinitis – had a greater diversity of fungi compared with healthy people, and it’s thought that these changes might affect how the body responds to pollen.
This study ‘demonstrates for the first time that the nasal mycobiota varies during health and allergic rhinitis’, the researchers said.
Hay fever is triggered by an allergy to pollen – immune cells called B lymphocytes (or B cells) mistakenly identify the proteins on pollen as a threat and make antibodies in response.
These antibodies bind to mast cells, which play a key role in the immune response. When someone with hay fever is exposed to pollen, their sensitised mast cells trigger the release of chemicals including histamine to rid the body of the ‘threat’.
Histamine makes blood vessels dilate, causing the stuffy nose, and prompts the release of fluid from tiny blood vessels, leading to a runny nose, sneezing and red itchy eyes.
In the new study, published in the journal Frontiers in Microbiology, scientists swabbed the nostrils of 125 healthy people and 214 with respiratory disease – allergic rhinitis; allergic rhinitis with asthma; or asthma alone (as people with hay fever often have asthma as well).
They found that the people with allergic rhinitis had a significantly more diverse population of fungi.
The researchers think that when the usual nasal mycobiome is changed, it might affect how the body responds to allergic triggers such as pollen.
‘Fungal cell wall components, and derived metabolites [which the fungi produce], are known to interact with immune cells, leading to the activation of various defence pathways that can either exacerbate or alleviate inflammation in the respiratory tract – potentially influencing the severity of allergic reactions,’ Luis Delgado, an immunologist involved in the study, told Good Health.
Previous studies have found differences in the nasal bacteria of people with hay fever, too, and the research team will now explore how the fungal and bacterial communities behave together.
Commenting on the new research, Dr Neil McCarthy, a senior lecturer in immunology at Queen Mary University of London, said: ‘If we can understand more about the microbial triggers that our immune system reacts to in allergic diseases, we might be able to develop better treatments.’
But hay fever is not the only health condition with a fungal link, says Dr McCarthy – Crohn’s disease, dermatitis, liver disorders, and even some cancers are thought to be linked to fungi.
‘Beyond specific types of infection, pretty much any disease where bacteria are thought to play a role, it’s likely that fungi are also involved – researchers have just tended to overlook them.
‘Like bacteria, fungi tend to live on our body surfaces and interact with the immune system in various ways that can influence our health.’
But though we have fewer of them, fungi are ‘made of much larger cells than bacteria, so they still account for a lot of the microbial signals that our body has to process every day, including some important chemicals that bacteria don’t produce’, says Dr McCarthy.
‘Most of the time fungi are harmless or even beneficial to us, helping to process our food and regulate our immune defences.
‘However, when their local environment changes – such as following a diet change or antibiotic treatments that reduce bacterial competition – they can act more like pathogens [that cause illness].
In the case of Crohn’s, Dr Steve James, a molecular microbiologist at Quadram Institute Bioscience, explains that the same fungus that causes thrush, Candida albicans, can exacerbate inflammation.
‘There was also a recent study which implicated a role for this species in long Covid,’ he adds.
The 2023 study, in Nature Immunology, found that Candida albicans flourished in the gut of patients with severe Covid, triggering an upsurge in immune cells in the lungs, which can worsen the inflammatory response already damaging these organs.
Fungus has also been linked to some neurological conditions.
Immunologist Dr Neil McCarthy believes that if scientists can understand more about the microbial triggers that our immune system reacts to in allergic diseases, they might be able to develop better treatments for hay fever
As Dr Becky Jones, from the charity Parkinson’s UK, told Good Health: ‘There is some evidence that some types of fungus are associated with a higher risk of developing Parkinson’s.’
A study by the University of Liverpool in 2021, for example, which compared stool samples of people with and without Parkinson’s, found a different fungal composition in their gut.
‘The majority of research seems to be around a fungus called Malassezia, which is associated with seborrhoeic dermatitis [a skin condition that often occurs on the scalp], a common problem for people with Parkinson’s disease,’ said Dr Jones. ‘However the mechanism behind any potential link isn’t known.’
Some small studies have also found links between fungus and depression, anxiety and schizophrenia. For example, a 2020 study at Zhejiang University in China, which compared stool samples from people experiencing a depressive episode with healthy controls, found the depressed group had less diversity of fungi, with higher levels of Candida and less Penicillium in particular.
‘It’s hard to unravel cause versus consequence in situations like this – a common problem with microbiome science,’ said Dr McCarthy. But an ‘imbalance of microbe species in the gut means altered patterns of chemical production by these organisms (including neurotransmitters such as serotonin).
‘These chemicals can act on human tissues and immune cells both locally in the gut and via the bloodstream or nerve cells to influence the brain and behaviour.’
While bacteria may have been getting most of the attention up until now, the vital role of fungus to our health is becoming increasingly apparent.
