Mould spores can be found everywhere, as they are very common in the environment, and there is almost constant exposure to airborne spores throughout the year. It can be found indoors and outdoors. Certain moulds can induce allergies in susceptible people. According to the American College of Occupational and Environmental Medicine, about 10% of people have a mould allergy, and about 5% show symptoms.
People with mould allergies experience symptoms throughout the year, although exacerbations may occur during wet and mild weather in the autumn.
An allergy to mould is far more serious than other allergies, such as a pollen allergy, as fungi can colonise the human body and may damage airways through the production of toxins, proteases and enzymes.1
Mould allergies can also trigger an asthma attack in people who suffer from asthma, or lead to the development of asthma. A study in Finland showed that exposure to mould in homes increased the risk of developing asthma in children by 2.4 times in the 6 years following exposure compared to those not exposed. Another study in Australia found that increased exposure to Cladosporium in homes increased the likelihood of development of adult asthma by 1.5 times.2
What is mould?
Mould is a type of fungus that produces airborne spores. Mould can grow on virtually any substance, and usually thrives in damp environments. It can be found indoors and outdoors. Spore concentration in the environment varies depending on climatic factors, such as wind, temperature, and moisture. The majority of moulds grow outdoors. The most frequent indoor moulds are Penicillium, Aspergillus and Cladosporium.1
As most moulds prefer damp conditions, they can be found in basements, under-sink cabinets, refrigerators, damp window sills, and in bathrooms, especially in shower stalls and on the shower curtains.
Causes of mould allergy
If your immune system overreacts to mould, it produces antibodies against the mould when you inhale the spores. Each time your body is exposed to the mould spores, it reacts more severely. Only certain moulds cause allergies, for example, Aspergillus and Cladosporium. Stachybotrys (black mould) is a toxic mould which can cause very serious illness. In addition, Aspergillus can also cause a serious infection known as Aspergillosis, especially in people with weakened immune systems or lung conditions.
Some people also react to mould in food or drink. Mould can be found in certain foods, such as fermented food, some cheeses, wines, and vinegar.
Some people are more likely to develop a mould allergy or be affected by mould. Those with a higher risk include:
- Babies and young children
- Older people
- People with preexisting skin conditions, such as atopic eczema
- People with a weakened immune system, such as those undergoing chemotherapy or radiotherapy
- People who have a respiratory condition such as asthma or chronic obstructive pulmonary disease (COPD)
- Those with a history of allergies
- People are exposed to mould over a long period of time, either through their job or living environment.
Symptoms of mould allergy
A mould allergy can cause respiratory symptoms, such as:
- A runny nose or congestion
In people with asthma, it may trigger an asthma attack. Mould allergies can also cause skin-related symptoms, such as dry skin and rashes. It may also cause symptoms such as itchy and watery eyes.
Some types of moulds can cause lung infections and anaphylaxis. There are also moulds which produce mycotoxins, which can produce severe symptoms and be fatal. Symptoms can include cancer, pregnancy complications and lung fibrosis.
Mould allergy and asthma
Studies have shown that a rise in mould spores is associated with increased hospital admissions and emergency room visits in people with asthma. The mould species implicated in higher hospital admissions were Alternaria, Cladosporium and Aspergillus. Mould spores can be spread by higher wind speeds, and spore production can be increased due to higher humidity. Therefore, thunderstorms have been associated with “thunderstorm asthma”. In a Canadian study, fungal spore counts doubled and emergency admissions increased by more than 15% on days with thunderstorms, with no increase in pollen counts being recorded during this time.3
As previously mentioned, other studies have shown that living in an environment with mould, especially Cladosporium increases the likelihood of developing asthma among children and adults.2
Diagnosing mould allergy
To diagnose a mould allergy, your doctor will take a look at your medical history and perform a symptom assessment. They may perform tests such as skin prick tests or blood tests.
A skin prick test involves pricking the skin with a lancet with small amounts of allergens or moulds applied to it. If the person is allergic to that mould, they will have a local reaction, such as itching, redness or swelling.
Management and treatment
For people allergic to mould, it is best to avoid exposure to mould outdoors and indoors. Some ways of reducing mould exposure outdoors would be:
- To avoid being in the woods when mould counts are high (in damp conditions)
- To remove dead plant material and leaves straight away
- To have someone else do garden work or to wear protective equipment, such as a N95 respirator and sunglasses, when gardening
- To avoid damp, musty buildings or buildings where hay or grain is stored
- To avoid country areas during harvesting, especially if it is windy
Some ways to avoid mould exposure indoors are:
- To use plenty of ventilation and thoroughly clean the bathroom, kitchen and utility rooms
- To clean mould from window frames and dry condensation, especially in the winter
- Not to dry clothes indoors or over radiators and make sure clothes are dry when placing them in cupboards
- Close internal doors when cooking, showering or bathing to avoid steam spreading through the house. It is also a good idea to use extractor fans and cooker hoods
- To treat any areas of dampness on walls
However, as mould is very common, it is difficult to avoid it completely. There are medications available to ease symptoms. These include antihistamines, which are used to block histamine that is released by the immune system in response to the mould. They are available as over-the-counter tablets, such as fexofenadine, cetirizine and loratadine, and as prescription nasal sprays (azelastine and olopatadine). Nasal corticosteroid sprays, such as fluticasone and ciclesonide, can be used to treat inflammation caused by a mould allergy and are some of the most effective allergy medications, as they don’t have serious side effects.
Oral decongestants and decongestant nasal sprays may also be used, but they should not be used for a long period of time as they may cause side effects. Montelukast has also been used to block leukotrienes, which can cause allergy symptoms. This medication is especially effective in people with asthma, but there have been concerns about some of the side effects of this medication.
Some patients may benefit from immunotherapy for long-term relief. This involves exposing the patient to small increasing amounts of the allergen over time, thus gradually increasing tolerance to the allergen. This should then reduce or completely stop the allergy symptoms.
Preventing and dealing with mould growth at home
If you see or smell mould in your home, you should remove it. Mould can be different colours and look like spots, and it may also smell musty. Small areas of mould can be removed using household products, such as soap and water, vinegar or household bleach. For large areas, you should contact the environmental health department for advice and help.
To prevent mould from coming back, you can use a dehumidifier. Humidity levels in your home should be less than 50%, and you can measure these using a hygrometer. Also, making sure there are no leaks in the house can prevent mould formation. You should also regularly ventilate the house and use extractor fans in the kitchen and bathroom. It is also a good idea to regularly clean the bathroom with an anti-mould cleaner.
People with a mould allergy have an immune system which overreacts when they breathe in mould spores. While some people may have only minor symptoms, others may have more severe symptoms. Some types of moulds are more likely to cause an allergy than others, and some may cause serious health issues and even be fatal.
The best way to prevent symptoms caused by a mould allergy is to avoid mould. However, as small amounts of mould can be found everywhere indoors and outdoors, it can be difficult to avoid. Treatment options include medications such as antihistamines, nasal corticosteroids, and immunotherapy. Mould increases the risk of developing asthma. Therefore, measures should be taken to remove any mould from the house and prevent mould from developing in the first place by controlling humidity levels and by keeping the house well-ventilated. There is no cure for mould allergy, but it can be managed by reducing exposure to it and taking the recommended medications.
- Simon-Nobbe B, Denk U, Pöll V, Rid R, Breitenbach M. The spectrum of fungal allergy. International Archives of Allergy and Immunology [Internet]. 2007 Aug 20 [cited 2023 Jul 28];145(1):58–86. Available from: https://doi.org/10.1159/000107578
- Park JH, Cox-Ganser JM. Mold exposure and respiratory health in damp indoor environments. FBE [Internet]. 2011 Jan 1 [cited 2023 Jul 28];3(2):757–71. Available from: https://www.imrpress.com/journal/FBE/3/2/10.2741/E284
- D’Amato G, Chong‐Neto HJ, Monge Ortega OP, Vitale C, Ansotegui I, Rosario N, et al. The effects of climate change on respiratory allergy and asthma induced by pollen and mold allergens. Allergy [Internet]. 2020 Sep [cited 2023 Jul 28];75(9):2219–28. Available from: https://onlinelibrary.wiley.com/doi/10.1111/all.14476