Mould allergy

Mould allergy is how the immune system responds to inhaling tiny particles released by mould, known as mould spores, which are a type of fungus. This reaction can lead to a range of allergy-like symptoms, often affecting the skin and respiratory system.¹ 

Symptoms include:

• Constant watery or itchy eyes
• Skin rashes
• Nasal issues: could be runny, congested, or irritated
• Respiratory issues: wheezing or shortness of breath
• An itchy throat
• Constant sneezing and persistent coughing
• Headaches
• Swelling
• Flu-like symptoms
• Symptoms that last several weeks, in environments where mould is likely to grow

Data from research and epidemiological studies indicate that fungi, including mould, are associated with respiratory illnesses. Mould can act as an allergen both indoors and outdoors. People with asthma are susceptible to mould exposure, with studies suggesting that mould exposure could increase the risk of developing asthma.¹ 

Where mould tends to grow indoors

Mould grows best in damp, dark, and poorly ventilated areas of the home. Common problem spots include:

• Bathrooms - The humid, moist environment created after showering, especially without proper ventilation or an extractor fan, can cause lingering dampness. This moisture can lead to mould growth on walls and ceilings
• Kitchens - Mould can develop near sinks, or anywhere where water is frequently used. Steam from cooking, no extractor fan, combined with little airflow, creates a perfect environment for mould
• Appliances - Washing machines and dishwashers are potential sources, especially if there are any leaks or if water collects in areas where it cannot fully dry

These indoor mould environments are particularly concerning, as they have been associated with the development and worsening of asthma, especially in children. Exposure to indoor mould has been linked to a higher frequency of coughing and more severe respiratory symptoms. Studies have even found connections between elevated mould spore levels and increased hospital visits, asthma treatments, and, in more severe cases, asthma-related deaths.¹ 

When to see a doctor

Persistent symptoms

If your symptoms do not improve after several weeks or seem to be getting worse, it is time to see a doctor. 

While there are millions of different types of mould, the majority of them are harmless to humans. However, some can trigger allergies, which can worsen asthma symptoms or even lead to more serious health issues. That is why it is important not to ignore ongoing symptoms, especially when mould exposure might be the cause. In many cases, people don’t even realise that mould spores are the cause of their allergic reactions or respiratory issues, and delaying medical attention can worsen outcomes.² 

Medical experts, particularly immunologists and allergists, have become increasingly concerned about the health risks linked to mould exposure. These health professionals often see patients struggling with mould-related conditions, which has raised awareness about the importance of early detection and intervention.³ 

Interference with daily life

If your symptoms are starting to interfere with everyday tasks, that is another sign to seek medical advice. This might include persistent fatigue, poor sleep, brain fog, or worsening breathing difficulties. If you are finding it harder to concentrate or go about your normal activities, a visit to your healthcare provider is essential, as these could be signs of an underlying condition that needs attention.

Respiratory health and mould

Mould can aggravate asthma symptoms and has been linked to the development of asthma, particularly in young children. An analysis of peer-reviewed studies found that both visible mould and mould odour were associated with the onset and worsening of asthma in children. However, the evidence in adults was less consistent, with fewer population-level studies available to draw firm conclusions. Despite this, workplace exposure to mould leads to occupational asthma, and experts agree that there is strong evidence supporting a link between damp indoor environments and certain respiratory health problems.⁴ 

For people living in rural areas, increased mould spore levels, especially during crop harvesting season, have been linked to breathing issues. There is also a rare condition called ‘thunderstorm asthma’, where spikes in fungal spore concentrations (particularly from Ascomycota and Basidiomycota species) during storms have been associated with asthma attacks.¹

If you are experiencing asthma symptoms, such as wheezing, ongoing coughing, chest tightness, or difficulty breathing, it is important to consult your GP. This is especially urgent if you have noticed visible mould at home and your symptoms began shortly afterwards.

Over-the-counter medications 

Another indication that you should speak to a doctor is if common standard allergy remedies, like antihistamines or nasal sprays, do not work or stop working. This could mean your symptoms are too severe, or that other underlying issues are preventing these medications from working. For example, frequent exposure to mould indoors or high mould spore levels in the air can overpower the effects of medication. In some cases, your body might even build up a tolerance to these drugs, making them less effective over time. 

Other external factors, such as air pollution, additional allergens like pollen, or hidden health conditions, can also affect how your body responds to treatment. That is why seeing a healthcare professional is important, as they can help rule out these complications and provide a more targeted and effective treatment plan.

What to expect

Medical history

When you visit your doctor to discuss possible mould allergy symptoms, the first step will usually be an in-depth discussion about your medical history and current health. Your doctor will review your general health records and ask if you have any existing conditions such as asthma or known allergies. They will also want to know if allergies or asthma run in your family since these conditions can be hereditary, meaning they are likely to occur if close relatives have them. Doctors may also ask about home and work environments to identify possible sources of mould exposure. Questions might include whether you’ve noticed visible mould in your living spaces, whether you work in damp or poorly ventilated areas, and what kind of outdoor activities you do that might expose you to higher mould levels.⁶

When it comes to symptoms, doctors will want to know which symptoms you are experiencing, when they started, how often they occur, and how severe they are. They will also assess whether the symptoms are affecting your daily life, for instance, whether it’s disturbing your sleep, affecting your performance at work, making it hard to keep up with everyday tasks, or affecting your mental health. All of this information helps them figure out possible triggers and whether mould is playing a role. Additionally, doctors might ask about any medications you’re currently taking or have recently used, both prescription and over-the-counter.

Possible tests

To help confirm whether mould is the cause of your symptoms, doctors may suggest one or more of the following tests:

• Physical examinations: Doctors might physically check your skin for rashes or listen to your lungs for any unusual breathing sounds, and will generally look for any signs of allergy
• Skin prick test: This is the standard allergy test where small amounts of suspected allergens (in this case, mould) are applied to your skin using tiny pricks. If a raised bump appears at any of the test sites, it suggests an allergic reaction to that substance⁷
• Blood test (IgE): This test measures the levels of mould-specific IgE antibodies in your blood, which are produced by the immune system in response to allergens, so high levels can indicate mould sensitivity⁷
• Lung function test: Also known as pulmonary function tests (PFT), it involves breathing into a tube to measure your lung capacity and overall lung health, particularly useful if asthma or respiratory issues are suspected⁷

Complications and difficulties in diagnosis

Both the World Health Organisation (WHO) and the Institute of Medicine have confirmed that indoor mould can pose a serious health risk. However, diagnosing mould-related illness isn’t always as straightforward as it may sound. It can be difficult to pinpoint the exact cause of symptoms, confirm whether mould is the trigger, or determine which specific mould is responsible. It might not be clear where the exposure happened, whether indoors, outdoors, at home, or at work. Mould exposure cannot always be measured accurately, and current testing methods may not always provide a clear answer. Due to this complexity, routine mould testing is not generally recommended, unless there is a strong suspicion based on symptoms and environment.⁶

Latest research on mould allergy testing

Researchers Kespohl et al. looked into the most effective way to diagnose mould allergies. They recommended that if mould allergy is suspected, the first step should be to perform a blood test to check for antibodies (sIgE) against a combination of common mould types, known as mx1. 

If mould-related asthma is a concern, further testing should be done, starting with specific IgE tests or skin prick tests for individual moulds, and ending with a bronchial challenge test, which checks how your lungs react to allergens and helps confirm asthma. For individuals with occupational mould exposure, especially those who test positive on Mx1, the researchers recommend a test for aspergillus fumigatus, which is a common mould found in workplace settings. On the other hand, if someone has respiratory or skin issues but there is no known mould exposure, the symptoms may be caused by other environmental allergens, not mould.⁶ 

Summary

Mould allergy occurs when the immune system reacts to airborne mould spores, causing symptoms like itchy eyes, rashes, nasal congestion, coughing, wheezing, and fatigue. Mould commonly grows in damp, poorly ventilated areas such as bathrooms, kitchens, and near household appliances. Persistent symptoms lasting weeks, especially with known mould exposure, require medical attention. Mould exposure can worsen asthma or lead to its development, particularly in children. If over-the-counter treatments fail or symptoms interfere with daily life, seeing a doctor is essential. Diagnosis may involve medical history, skin prick tests, IgE blood tests, or lung function tests. Although mould-related illnesses can be hard to diagnose, early detection and targeted treatment improve outcomes.