What are fungal spores?

There are thousands of different fungi in the world which are essential for the survival of other organisms. Unfortunately, fungi produce lots of spores that can also be detrimental to humans.

Health effects of fungal spores

Many fungal spores contain allergens which can trigger a range of respiratory symptoms in those susceptible.  These symptoms include 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 get allergy symptoms from fungal spores, including the majority of asthma sufferers.  Many fungal spore types have similar allergens which are released at different times of the year.  This means that sufferers of fungal spore allergies are likely to be sensitive to many types for large parts of the year.       

Main types of fungal spore

Fungi come in a wide range of types and sizes, most are microscopic but some, such as mushrooms and bracket fungi, are quite large. Fungal spores themselves are all microscopic, some as small as two micrometres in size. Most fungi require warmth and humidity to grow, reproduce and release their spores into the environment. Many fungi produce only small amounts of spores which rarely get airborne in quantity. However, some species are very prolific and widespread, producing high concentrations of spores which are readily dispersed into the atmosphere. The main types that trigger most symptoms in allergy sufferers are: Alternaria, Cladosporium, Epicoccum, Aspergillus, Penicillium, Didymella, Pleospora and a group of species collectively referred to as Basidiospores. Also important to asthma sufferers are Sporobolomyces and Tilletiopsis, which are very small spores produced primarily during warm, humid nights. 

Seasonal Spore Summary

Fungal spores are released on a seasonal basis. Many types can be found in the air all year round, typically peaking in the summer or late autumn.

Allergenic fungal spore calendars

These show the monthly average totals of spores per cubic metre of air, for the five year period, 2006-2010. The concentrations of spores produced by fungi vary greatly. For example, the Alternaria peak monthly average spore concentration is 3400, while for Cladosporium it is 210,000 and for Didymella 35,000. As a result, the thresholds for symptoms will also vary. However, thresholds have only been ascertained for Alternaria and Cladosporium so far. 

The calendars have been produced by averaging 5 years of data collected in Worcester. Worcester is located in the centre West of the country and receives high amounts of pollen and spores due to very suitable weather and sources. Although the trends shown will be similar for much of the country, the average amounts will tend to be lower in western coastal regions and mountainous areas. The spore seasons in Northern Ireland, Scotland and the far North England will also start a few days to two weeks later than in the more southerly regions. A weekly spore forecast for spores is available here. 

Alternaria

The first high days (>50 spores per cubic metre of air, daily average) start occurring in July. The peak average monthly total occurs in August (3400 spores) then in September high counts continue but go into decline.

All other months are very low. Download the Alternaria seasons charts from 2020 to 2022.

Cladosporium

November to March are very low for this type. The high threshold (>3000 spores per cubic metre of air, daily average) starts to be reached in late May. In June, the average monthly total reaches 104,000, in July 210,000 and in August 152,000. The spores go into decline in mid-September, with just occasional high days during warm weather.

Didymella exitialis

October to May are very low for this type. The peak period is well defined, starting in late June and reaching peak period in July, which continues through August with a monthly average peak total of 35,000 spores.

There may be a few high days in early September then the risk drops to very low.

Aspergillus and Penicillium types

The year starts with a high risk for these types with a total monthly average of 1,333 spores in January and 1,215 in February. Spores continue to be airborne during Spring and early Summer but possibly below the levels needed to trigger symptoms. From mid-August the risk starts to rise again and people often report various respiratory symptoms during warm and humid conditions in late August, September and October, with the peak reaching an average of 1,950 spores in October. Aspergillosis sufferers report symptoms worsen in late Feb/March and again in August through to late October, with October the worst month. Although the spore levels continue to be high during November and December, few people report symptoms, so it is likely that the types occurring during these months are less allergenic. 

Basidiospores

The peak monthly total occurs in September for this type at 32,350 spores, after gradually increasing over the summer months. October is also a peak month, with a similar total.

The risk drops rapidly down to low by December. January through to early June are low for these spores. 

Epicoccum

January to early June remain low for this type, with the increase starting during warm weather from mid-June.

The peak monthly total occurs in August at 1,218 spores, September sees a similar high at 1,000 spores and then the season goes into decline through October, returning to low in November and December.

Leptosphaeria 

Leptosphaeria (or Phoma) fungi mainly occur in crop-growing areas (especially where one of their major hosts, oilseed rape, is grown). The spores are liberated during or after rain and are rarely present during dry weather. Spores can be emitted at any time of year during rainfall but the levels really start to increase during wet weather in April and May, continuing at a high risk until late October or early November. Very dry months have lower levels of Leptosphaeria compared to the average.

Pleospora

This type is low in January then there is an increase through February and March culminating in a peak in April and May (590 & 540 spores, respectively).

Thereafter, the risk drops off back to low levels from late June onwards. 

Pollen Calendar Reference:

Sadys M, Adams-Groom B, Herbert RJ, Kennedy R. (2016) Comparisons of fungal spore distributions using air sampling at Worcester, England (2006-2010). Aerobiologia, 32(4): 619-634 

Spore levels show trends throughout the year:

Spring: 

In the Spring, most spore types are at low levels, apart from Pleospora. Cladosporium and Tilletiopsis can start increasing in May if the weather is warm and dry.

Summer to early Autumn:

The spore risk starts to rise in mid-June with the increase in temperatures. The risk peaks in late June/early July and continues until late September. Typically, during the day, there will be the ‘dry-weather’ spore types of Alternaria & Cladosporium and some types of Penicillium and Aspergillus. ‘Wet-weather’ spores 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. In addition, rainfall will help the production of spores which are then released after heavy rain or during light showers or drizzly rain. There is a lower spore risk in very windy, unusually cold and dry weather. When late August and September are warm and humid, Penicillium and Aspergillus types can become very problematic for those affected by them, triggering a range of symptoms including hay fever, mucous production, cough, wheezing and asthma. 

Mid-Autumn: 

Penicillium and Aspergillus types can continue to be quite high into October - and even November and early December if temperatures remain mild. There are usually some of these spores present in the air throughout the Autumn and even lower levels can trigger some symptoms. Many other spore types are starting to decline, but the risk can be moderate to high on warmer, humid days. By the end of November, the risk decreases to low unless it is very mild and damp. The lowest risk is on dry, cold frosty days. Spores from mushrooms and bracket fungi reach their peak at this time of year, particularly in rural areas, although the risk is low to moderate for most spore sufferers as these are milder allergens.

Winter: 

Aspergillus and Penicillium types quite often have a second peak in January and early February. Other spore types are low in Winter, although Pleospora can start increasing from February.

Types of Spore