Inhaled fungal spores are a well-known cause of allergy and asthma. Indeed in some places the rate and severity of asthma in the population have been linked to airborne levels of the mould spores Alternaria and Cladosporium. Allergy to these fungal spores is an important cause of severe seasonal asthma in the late summer and autumn (see below).  Patients with this type of allergy may have severe episodes of asthma at the same time each year, and may even require hospital admission.  However the fact that there is a potential environmental cause of the problem usually goes unrecognised, unless the patient is seen by an clinical allergist.  An awareness of these and other allergen triggers can allows preventive treatment either by avoiding the troublesome circumstances, or at least ensuring maximal prophylactic measures (e.g. adequate preventer inhaled steroid) at the appropriate time.

Spores, hay fever and asthma

Dr Harry Morrow-Brown

Allergens such as pollen grains and fungal spores cause allergic reactions when inhaled because they land on the sensitised lining of the nose, the conjunctiva of the eye, or the mucous membranes of the airways.

The main causes of hay fever are tree pollens from March to June, grass pollens in June and July, and mould spores from July to October. The moment a pollen grain or mould spore lands on the moist lining of the nose, the conjunctiva in the eye or the mucous membrane lining the bronchial passages, the allergen begins to leak out of it. If there is an allergy, sneezing occurs at once in an attempt to get rid of the allergen. Release of the allergen from the pollen grain or mould spore happens very quickly, and the repeated inhalation of thousands of pollen grains or mould spores day after day causes incessant sneezing, itchy eyes, and sometimes asthma.

In the damp British climate the pollen season is succeeded by the mould spore and yeast season which lasts until late October. Hay fever, and especially asthma, also occur at this time, and are even more closely linked to the weather.

Millions of mould spores get airborne during the day, especially in the afternoon, and because spores are much smaller than pollen grains they get inhaled into the depths of the lung. In the early hours of the morning billions of yeasts appear in the air, especially in low-lying river valleys. When there is a spell of wet and damp weather enormous numbers of yeasts in the air will persist through the day. These patients are better to keep the windows shut at night.

The season for mould spores extends well into the autumn and causes not only hay fever, but also seasonal asthma. The season is much longer than for pollen only, often not ceasing until the first frost. A hard frost seems to be an unusual event in recent years, perhaps due to global warning.

Research by the Midlands Asthma and Allergy Research Association in Derby over many years has established the importance of mould spores in the causation of asthma. The charts that follow are from research carried out in this unit.

The first charts show what contribution individual mould spores make to the severity of asthma by taking daily spore counts per cubic metre of air and comparing them with the daily Peak Expiratory Flow Rate as recorded by the patient.

As the spore counts go up the peak expiratory flow rate (PEFR) readings go down. These observations were made 30 years ago and would be difficult to repeat today as more effective modern asthma treatments would suppress these responses (charts from the Midlands Asthma and Allergy Research Association).

Whilst the relationship between individual mould spores and symptoms is interesting, what is demonstrated is more likely to be a general relationship to spore counts across a number of species as shown by the chart below.

The same weather conditions trigger the release of many types of spore into the atmosphere. This makes it difficult to be sure which spore is causing asthma or hay fever in the individual case (charts from the Midlands Asthma and Allergy Research Unit).

© Dr. Harry Morrow-Brown. All Rights Reserved.

Symptoms and spore counts

Dr Harry Morrow-Brown

The charts below show the relationship between spore counts and symptoms as recorded by actual patients. The clear relationships between symptoms and mould spore counts are clearly visible.

In this case of seasonal asthma, a relationship between respiratory symptoms and three moulds was shown by bronchial provocation test, the allergy skin tests to the same moulds were negative. The patient was allergic not only to the moulds Botrytris and Phoma, but also to the yeast Sporobolomyces which gets into the air in huge numbers in damp weather in the UK in July and August, especially in the early morning hours (charts from the Midlands Asthma and Allergy Research Association).

© Dr. Harry Morrow-Brown. All Rights Reserved.

Seasonal patters

The following charts shows how between them tree pollens, grass pollens and mould spores can cause symptoms intermittently or continuously, from April to October in those unlucky enough to suffer these allergies. Some trees pollinate even earlier than this (e.g. hazel yew and alder), so that hay fever can, for some, start even as early as the end of January (see pollen chart).

Allergy to fungal infections

Exposure to fungi is also known to be capable of causing asthma in other ways. Occasional patients can be shown to have evidence of a fungus present in the lung (for example, discovered when their sputum is cultured) and then have severe asthma symptoms as a result, a condition known as bronchopulmonary aspergillosis. Courses of antifungal drug treatment may then be helpful.

Equally as intriguing is the very occasional asthmatic patient with an athlete's foot infection who is found to be allergic to the Trichophyton fungus that is causing it, and who responds to antifungal treatment. This course of treatment may then clear not only the athlete's foot, but also the asthma.  Fungal foot infections are also very occasionally thought to cause chronic urticaria.