Mould is a type of fungus that grows in damp environments, both outdoors—where it peaks in summer and fall—and indoors on wet surfaces like drywall. Factors such as flooding, leaks, high humidity, and poor ventilation promote mould growth inside homes and buildings.

While most moulds are harmless and even useful for making foods and medicines, some can harm health by releasing spores (allergens) that irritate the respiratory system and trigger severe allergic reactions. Allergens are the substances that cause allergies (here, fungal spores are allergens).¹

Fungal allergens commonly trigger respiratory and skin symptoms, affecting 5–20% of patients presenting to allergy clinics.²

It is essential to recognise the early signs of mould allergies to prevent severe reactions, such as asthma, cancer, and cognitive impairment. In this article, we’ll discuss 10 signs of mould allergies that can alert you to see a doctor.

1. Frequent sneezing and wheezing

Mould spores are tiny reproductive substances produced by the moulds that can enter through the nasal cavity, causing irritation. This activates the immune system and may cause:

• Sneezing: The release of the inflammatory chemicals called histamines from the immune system triggers a reflexive action to clear the allergen. This process is called sneezing, which forces out the allergen through the nasal cavity. If you notice that sneezing episodes increase in a damp and moist area, you can understand that you have got a mould allergy
• Wheezing: The narrowing of the airways produces a whistling sound, which is called wheezing. In adults and older children, wheezing around dampness or mould usually indicates an allergic reaction, though very high exposure can also cause irritation³

Wheezing has been consistently found to be associated with indoor dampness in all age categories, although the presence of other indoor allergens, such as dust mite in damp conditions, makes it difficult to identify the specific mechanism.

2. Runny or stuffy nose

Mould spores can irritate your nasal tissues, causing a continuous runny and stuffy nose. This is elevated in a closed, damp room (the area suspected of mould growth). This can ease out when you move out of the room into fresh air. In this way, you can differentiate between a common cold and mould allergies. 

Wieslander et al. (1999) reported that wet concrete floors were associated with an increased risk of an irritated or stuffy/runny nose. Some studies show that damp indoor environments are linked with symptoms like a reduced sense of smell.³

3. Itchy, watery eyes

When fungal spores get on the thin membrane covering your eyes (conjunctiva), they can induce an allergic response. In response to this the immune system gets activated. The eyes become red, swollen, watery, and itchy. If there are no other irritants, like smoke or pet fur, and you’re still getting red, itchy eyes, you have mostly got mould allergy. 

For instance, in large surveys, visible mould or damp damage in homes was consistently associated with increased risks of common colds and nasal or eye irritation, even when controlling for other factors like smoking and pets.³

4. Coughing and throat irritation

Cough and throat irritation are common in many diseases affected by viruses and bacteria. Inhaling mould spores can also cause similar symptoms. 

A few studies have mentioned correlations between indoor dampness and visible mould with increased prevalence of respiratory infections and allergic symptoms in children and young adults. It can cause throat infections, ear infections, and chronic infections like allergic rhinitis.

For instance, a study involving telephone interviews and indoor air measurements revealed that visible mould or mildew in homes was associated with the persistence of first-year infants to cough no matter whether the mothers had asthma or not. In particular, increased coughing was related to a high air concentration of Penicillium (a mould).³

5. Worsening asthma symptoms

Mould is a trigger agent for asthma causing inflammation and constriction of the airways with excessive mucus. If you feel chest tightness or breathlessness, a mould allergy could be a possibility. 

High moisture content indoors and use of contaminated humidifiers can increase the allergens in the air. This can further worsen the symptoms of diagnosed asthma. 

Research finds that a damp and mouldy environment can worsen asthma symptoms in individuals with diagnosed asthma. 

Two case-control studies observed exposure to visible mould or mould smell at home or work as a probable risk factor for developing adult-onset asthma, despite the adjustment of other factors. Although one of the studies did not reveal any significant correlation with visible dampness alone, both of them had consistent results reporting a correlation between mould presence and the development of asthma.³

6. Skin rashes or irritation

Direct contact with the spores of the mould causes skin reactions, particularly in people with eczema. Touching mould-contaminated surfaces, like bathroom tiles, and damp walls can trigger itchy rashes. Some studies identified some connections between dampness or mould and overall skin irritation.

Studies also show that people with low immunity are susceptible to fungal infections. Although eczema and atopic dermatitis, which have intense itching and red skin, have been implicated in moisture-prone indoor conditions, they are often allergically induced and are susceptible to history and appearance.

7. Sinus headaches

Mould spores can cause sinus congestion and severe headaches. You might also feel dull pain and pressure around your forehead and behind your eyes. Some sinus infections can improve temporarily, however, it may return back with mould exposure.

Fungal colonisation is common in both healthy individuals and those with sinus issues, posing risks of headaches and sinus infections.

8. Fatigue

The immune system constantly battles with mould allergens leaving the body weak and tired. Many people face decreased energy, which can improve with a changed environment. 

Research shows that mould exposure can trigger the release of inflammatory cytokines like TNFα and IL-6, which may contribute to symptoms such as fatigue. 

In one study, over half of the volunteers who inhaled endotoxin (similar to toxins produced by mould) reported unusual tiredness, possibly linked to TNFα activity.

Additionally, fatigue often occurs alongside chronic rhinosinusitis, raising the possibility that shared underlying factors, rather than mould alone, might explain some reports of tiredness.

9. Digestive issue

Moulds can cause several gastrointestinal problems such as diarrhoea and nausea. This is evident if moulds are present in kitchen or food storage areas. 

A review noted that eating mycotoxins in mouldy foods can cause nausea, vomiting, and diarrhoea, and while some people exposed to damp indoor environments report similar symptoms, few studies have rigorously assessed this connection. 

Most research found only nonsignificant increases in gastrointestinal complaints. One early study showed higher rates of nausea and vomiting in children.³

10. Shortness of breath

Dyspnea, or shortness of breath, is a common symptom in people with respiratory or heart conditions and can also result from breathing high levels of endotoxins. 

Studies consistently find that living in damp or mouldy indoor environments is linked to dyspnea, though only a few studies have specifically examined this connection. 

Overall, there is limited evidence supporting an association between damp environments and dyspnea. However, some data shows that moulds and dampness are the major reasons for this.³

How to differentiate mould allergy from other diseases?

The most obvious sign of mould is the appearance of black, green, orange, or white patches growing on walls, ceilings, wood, or carpets, particularly in damp areas like bathrooms, around leaking water heaters, or neglected plaster repairs.

• Relief of symptoms when spending time outdoors or elsewhere:
  One of the most telling signs of a mould allergy is that your symptoms improve when you leave the suspect environment—such as during vacations or extended time outdoors
• Reoccurrence when returning to the contaminated environment:
  When you return home or to your workplace, your symptoms often recur within hours or days, strongly suggesting an environmental trigger, such as mould

What can you do about it?

1. Check for mould: Look for musty smells, visible mould, or damp spots
2. Boost airflow: Use fans, open windows, and keep indoor humidity
3. Fix leaks quickly: Dry everything within 24–48 hours
4. Clean smartly: Wear masks and gloves when scrubbing mould
5. Use HEPA filters: These reduce airborne spores
6. Consider allergist testing: Skin prick or blood tests can confirm mould allergies
7. Get medical help: Doctors can prescribe antihistamines, nasal sprays, or allergy shots (immunotherapy)

FAQs

How do you test for mould allergy?

A mould allergy may be screened via:

• A skin prick test in which small doses of mould allergens are put on your skin to determine whether you react to them or not
• A special IgE test (blood test) can also be performed as a way of assessing the immune reaction towards mould proteins

What happens if you are exposed to mould for a long time?

If exposed for a longer time, it can cause chronic respiratory issues, including chronic coughing, wheezing, or asthma. It may also cause a chronic allergic reaction, exhaustion, and possibly infections among individuals whose immune systems are compromised.

What are the signs of mould sickness?

Mould sickness has signs such as sneezing, runny nose, itchy eyes, rashes on the skin, coughing, and wheezing. Others can also develop headaches, tiredness, or their asthma can be aggravated.