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What are fungal spores?

Fungal spores are microscopic biological particles that allow fungi to be reproduced, serving a similar purpose to that of seeds in the plant world although the mechanisms are different. Fungi, including moulds, are an important component of the ecosystem. They obtain their nutrients by feeding on or parasitizing all kinds of substrates and are essential for the recycling of minerals and carbon by the decomposition of organic debris and waste.

Spores of Alternaria

It has been estimated that fungi recycle millions of tons of organic waste annually. Life for other types of organism would come to a virtual halt without the activity of fungi. In addition, mushrooms and other fleshy fungi are a source of nutrition for many animals, including Humans. There are thousands of different fungi in the world but some types are found in most regions while others can be specific to just one or two hosts.

Health effects of fungal spores

Many fungal spores contain allergens which can trigger a range of respiratory symptoms in those susceptible, including sneezing, runny nose, mucous production, cough, congestion, sinusitis, earache, headache, wheezing, asthma and a range of bronchial symptoms and diseases. It is estimated that around 3-4% of the general population and 10% of atopic people get symptoms from fungal spores while the majority of severe asthma sufferers are allergic to them. A number of fungal spore types share similar allergens which means that those who are allergic to moulds are likely to be sensitized to multiple types. Due to the fact that the different fungi vary in the release times of their spores, some people can therefore be affected for large parts of the year.

Golden brown spores of the bracket fungi, Ganoderma sp.

The main fungal spore types triggering allergy and asthma in the UK are Alternaria, Cladosporium, Aspergillus/Penicillium and Didymella. Allergic responses to each spore type differ between individuals and the allergens vary in the severity of the allergic reaction they induce. More people are allergic to Alternaria than Cladosporium, for example, even though the latter is much more common in the air. Alternaria also produces more strongly positive reactions while Cladosporium tends to produce a milder allergic reaction. However, Cladosporium, and in particular Cladosporium herbarum, is often the major contributor to air-spora and due to its high concentrations is therefore a major cause of inhalant allergy and allergic asthma in humans. Didymella exitialis is implicated in cases of severe asthma and also cross-reacts with Alternaria. Didymella exitialis grows on cereal crops, particularly wheat and barley so the risk can increase around harvesting of these crops. In addition, Basidiospores from mushrooms, toadstools and bracket fungi and some types of yeast (e.g. Sporobolomyces and Tilletiopsis) can also be problematic.

Fungal spore seasons in the UK

Fungal spores are released and distributed in a variety of ways and have specific climatic requirements. Some types favour warm, dry weather and are wind-dispersed and the numbers of these can be very high in the outdoor air. Examples of these ‘dry weather’ spores include Cladosporium, Alternaria and Epicoccum. Other types need certain temperature and moisture thresholds to be reached before they are released, so a warm, humid period can also produce a high spore risk. Examples of ‘wet weather’ spores include Didymella, Sporobolomyces and Tilletiopsis which are often abundant on mild, humid nights in Summer.

Seasonal Spore Summary

Fungal spores are mainly seasonal in their release but many types can be found in the air all year round typically peaking in the summer or late autumn.

A weekly summary and synopsis is always available on our website while the following gives an overview of the typical progression of spore levels throughout the year:

Spring: Fungal spores are generally low in number but the risk can rise to moderate in the late Spring if conditions are favourable.

Summer to early Autumn: The spore risk starts to rise in mid-June with the increase in temperatures and in late June/early July the risk starts to peak and continues until late September. Typically, during this season, there will be the ‘dry-weather’ spore types of Alternaria & Cladosporium and some types of Penicillium and Aspergillus and others by day and then the ‘wet-weather’ spores that respond to the dew during the night, such as Didymella, Sporobolomyces and Tilletiopsis. Therefore, there are a wide range of types that can affect people during each 24 hour period and many of the types have shared allergens that cross-react. In addition, rainfall will help the production of spores which are then released later after the rain (if it’s heavy) or during light showers or drizzly rain. Very windy weather tends to dilute the spores in the air and unusually cold, dry weather will lead to a lower spore risk.

Mid-Autumn: many of the main allergenic types are going into decline but there are still plenty of spores around and the risk can be moderate or even high in October on warmer, humid days. In November, the risk decreases to low by the end of the month unless it is very mild and damp. The lowest risk is on dry, cold frosty days.

Winter: Winter can be okay for some sufferers of fungal spores but for those sensitive to Penicillium and Aspergillus there will be some risk, particularly in January and early February.

A spore calendar is available from the website of the Midlands Asthma and Allergy Research Association at:

Habits and seasonality of the main allergenic spore types in the UK


Habitat / Substrates: Manyt outdoor substrates including soil, seeds and plants. Some species of Alternaria are also important crop pathogens. For example, A. brassicae causes leaf spot on brassicas and A. solani causes early blight of potatoes. Indoor substrates include foodstuffs, carpets, textiles and window frames. Mould colonies are usually black or grey.

Season: Main season July to September but may occur at other times of year and can occur in the winter indoors.

Allergenicity: High.


Aspergillus/penicillium spores

Habitat / Substrates: There are many different species of Aspergillus and Penicillium and they have a very wide range of substrates and tolerance. Examples: A.flavus grows on corn and peanuts, A. fumigatus grows in composts, mild to warm soils and on cereals, P. chrysogenum is found widely in nature, indoors it is found on food and is also the type used to produce Penicillin and P.expansum is a crop pathogen, causing post-harvest rot in apples.

Season: Throughout the year, with a small peak in August/September and the highest peak January/February.

Allergenicity: High for some types, particularly A. fumigatus and P. chrysogenum. A fumigatus is major cause of aspergillosis (farmer’s lung).


Cladosporium spores.

Habitat / Substrates: Outdoors on a wide range of plant substrates and in soil. Indoors, on paint and textiles. The mould colonies are generally black or olive-brown to brown.

Season: April to November and peaking in July and August. Occurs in low concentrations at all other times of year.

Allergenicity: High.


Didymella spores

Habitat / Substrates: Didymella exitialis occurs outdoors and is widespread on grasses and cereals, particularly wheat and barley. D.bryoniae attacks cucurbits and D.lycopersici causes tomato stem and fruit rots.

Season: June to September.

Allergenicity: High. D.exitialis has been demonstrated to induce asthma.


Epicoccum spore

Habitat / Substrates: Outdoors, widespread on soil and plant debris. Indoor substrates include paper and textiles.

Season: Main season August and September but may occur at other times of year in low concentrations.

Allergenicity: High.