Introduction

When we hear about mould allergies, we typically imagine sneezing, congested noses, or itchy eyes due to airborne mould. But what a lot of people don't know is that certain foods can actually exacerbate mould allergy symptoms. This is because moulds are not only in the air we breathe, but can also be in the food we consume.

This article examines the various foods that can cause or exacerbate mould allergy symptoms, how and why it occurs, and what to avoid if you or a loved one has an allergy to mould. Knowing these connections can assist you in making safer food options and better managing mould-related allergies in your daily life.

What is mould?

Moulds are a fungus that thrive both inside and outside the home, particularly in areas that are warm, humid, and wet, such as bathrooms, basements, and laundry rooms. Moulds grow by circulating spores through the air, and we're continuously exposed to them in the air we inhale, the food we consume, and occasionally even through contact with our skin. Although most fungi coexist harmlessly with humans, a few have the potential to cause health issues, particularly when the immune system overreacts.^1,2

The four most prevalent mould species leading to allergic reactions are Alternaria, Cladosporium, Aspergillus, and Penicillium. In certain areas, particularly Europe, Cladosporium is a significant allergen in children, whereas Alternaria prevails in the Mediterranean.³

Mould allergies occur when the immune system responds to mould proteins as if they were a threat, causing reactions such as sneezing, coughing, or even asthma.¹ 

Mushrooms

Mushrooms are one of the edible fungi that belong to a family of fungi known as basidiomycetes and ascomycetes. They are healthy, contain no cholesterol, and can be consumed as a fine source of protein. Yet, mushrooms can cause an allergy in some individuals.⁴

When they release spores into the atmosphere, they can serve as inhaled allergens just like pollen or mould spores. In a few instances, humans directly develop allergies to mushrooms when they consume them. More commonly, though, these reactions are not due to the mushroom itself, but because mushroom proteins are similar to proteins in airborne moulds. The immune system becomes confused and responds to the mushrooms as if they were the moulds to which an individual is already allergic. This phenomenon is referred to as cross-reactivity.⁴

Some individuals who are sensitive to airborne moulds such as Alternaria alternata and Cladosporium herbarum can also be sensitive to a few foods, including mushrooms and spinach. Such a relationship is referred to as "Alternaria-spinach syndrome", which occurs due to cross-reactivity. ^4,5

Some people may experience a reaction to raw mushrooms, but not to canned mushrooms that are processed at high temperatures. This is most probably due to the destruction of the allergy-causing proteins, most notably heat-sensitive ones.⁶

Mycoprotein

Mycoprotein is a high-protein food produced using a type of fungus and is often used as an alternative to meat. One such product, which is sold widely, is Quorn, produced using the fungus Fusarium venenatum. It was initially marketed in the UK in 1985 and has since been marketed in the US, Europe, Asia, and Australia. Quorn foods are marketed as healthy because they're rich in protein and essential amino acids while low in fat, cholesterol, sodium, and sugar.⁴

Not everyone, however, is tolerant of mycoprotein. Since the introduction of Quorn, numerous reports of adverse effects have been made after consumption. These have ranged from skin disturbances such as itchiness to swelling of the lips or throat, difficulty breathing, and in extreme cases, full-blown allergic reactions such as anaphylaxis. Others have had gastrointestinal problems like nausea, vomiting, diarrhoea, or abdominal cramps. A concern is that the majority of these reactions occurred after the first consumption of Quorn, suggesting that the immune system may be confusing it with other allergens, possibly due to its resemblance to mould or fungi.⁴

Fermented foods

Fungi have been utilised in food preparation for a long time, particularly in fermented foods such as cheese, soy products, and alcoholic beverages. They help improve the shelf life and nutrition of food and reduce the cooking time. For example, Penicillium species are used to produce blue and soft-ripened cheese, Monascus for red yeast rice, and Aspergillus and Rhizopus for soy products such as miso and tempeh. Although these fungi contribute to food production, they can also be allergens and trigger responses in sensitive people.⁴

Yeasts such as Saccharomyces cerevisiae are generally used to make alcoholic drinks. Although it is unusual to experience allergic reactions to beer or wine, and the blame is usually placed on the grains or the grapes, the yeast may actually be the culprit, particularly for those already sensitive to moulds. A number of mould-allergic patients responded to foods containing yeast, such as beer, wine, and sauces like pasta yeast sauce. Such reactions were occasional, for example, anaphylaxis, and tended to occur in autumn when there was a natural increase in the amount of mould in the air. This implies that inhaling mould spores can sensitise the body further to those proteins in food.^4,5

Some individuals are allergic but do not react to heated forms of these drinks or baked bread. This could be because heat inactivates the allergens.⁴

Fermented foods such as sausages have also triggered allergic reactions in some individuals.⁴

Foods infested with fungi

Fungi have a natural tendency to degrade organic matter; hence are usually the culprits when it comes to spoiling food. Fungi that infect food while in storage or being processed can cause allergic reactions or produce toxic substances known as mycotoxins. These mycotoxins are poisonous chemicals produced by moulds and may be used as indicators of poor food quality or contamination.⁴

Even individuals who were not allergic to some foods before may react suddenly if these foods become contaminated or mouldy.

Mould can also contaminate health supplements. Bee pollen supplements, for instance, might have mould spores such as Aspergillus or Cladosporium, which may induce severe allergic reactions in sensitive people.^4,5

In one study, individuals with asthma and mould allergy to Alternaria without any food allergies experienced allergic reactions simply by chewing sunflower seed shells open. The problem was not the seeds themselves but the mould on the shells. "Sunflower Seed–Fungus Syndrome" was the name given to this.^4,

Plant products

Plants are constantly under attack by harmful microorganisms, including fungi, bacteria, and viruses. They produce natural defence proteins known as pathogenesis-related proteins (PR-proteins) to defend themselves. Certain of these proteins, including thaumatin-like proteins (TLPs), have antifungal activity. Surprisingly, most of the proteins responsible for cross-reactive allergies between airborne mould and food of plant origin belong to this same category.⁴

Alternaria fungi species can infect fruits and vegetables without even showing signs of mould. For instance, scientists discovered that kiwis contaminated with Alternaria had both the allergen of the mould as well as the defence protein of the kiwi. Both proteins not only co-occurred in the kiwi pulp but also had interactions between them. The mould's allergen protein inhibited the kiwi's antifungal defence. Such interaction can result in what is referred to as cosensitization, such that an individual who is allergic to Alternaria would equally respond to infected fruit despite its appearance of being fresh. The same applies to other fruits like peaches and bananas, which also secrete similar PR proteins.⁴

In another study, 30% of individuals with atopic dermatitis (eczema) were sensitised to mould allergens and were also more likely to develop food allergies, particularly to nuts and sea fish.⁴

Summary

People with mould allergies often react not just to mould in the air, but also to certain foods. This is because some foods naturally contain fungi, while others become contaminated during storage or processing. These exposures can trigger allergic reactions, especially in individuals with sensitive immune systems.

Mushrooms and fermented foods like cheese, soy products, beer, and wine may cause reactions due to shared proteins with airborne moulds. Sometimes, the immune system gets confused and reacts to these food proteins as if they were mould. Cooking often reduces this risk by destroying heat-sensitive proteins.

Mould contamination in foods can also induce allergic reactions, even among individuals who had previously tolerated the food in question. 

Finally, fruits infested with mould can appear normal but possess allergens. In people who are sensitive to mould, these silent exposures can produce symptoms when the mould reacts with the fruit's inherent defence proteins. Awareness of the silent dangers makes it possible to better control mould allergy through wiser food selection.