When people experience ongoing congestion, coughing, headaches, fatigue, irritated eyes or worsening asthma, they naturally look for something happening inside their bodies.

But sometimes, an important part of the answer may be found in the environment around them.

Indoor mould can develop quietly behind walls, underneath flooring, inside cupboards, around windows or wherever moisture has been allowed to remain. It does not always form an obvious black patch. Sometimes the first warning is a persistent musty smell, recurring condensation or a room that never feels completely dry.

What Is Mould?

Mould is a type of fungus that reproduces by releasing tiny spores into the air. These spores exist naturally indoors and outdoors, but they can begin growing on household surfaces when moisture, warmth and suitable organic material are present.

Mould may grow on:

• Timber and plasterboard
• Carpets and curtains
• Furniture and clothing
• Books, cardboard and stored belongings
• Bathroom ceilings and window frames
• Walls affected by leaking roofs or plumbing

Mould can appear black, green, white, grey, orange or brown. Its colour does not reliably tell you whether it is more or less dangerous.

How Can Mould Affect Your Health?

The health effects of mould exposure vary considerably from one person to another.

NSW Health identifies possible effects including:

• A blocked or runny nose
• Irritation of the eyes or skin
• Coughing or wheezing
• Aggravation of asthma
• Asthma attacks in sensitive individuals

The World Health Organization has also found that damp or mould-affected buildings are associated with increased respiratory symptoms, allergies and asthma.

Some people report broader symptoms such as fatigue, headaches, poor concentration or feeling generally unwell while living or working in a damp building. However, these symptoms are not specific to mould and can have many possible causes. They should not be self-diagnosed as “mould illness” without appropriate medical investigation.

Rarely, serious fungal infections can occur, particularly in people with severely weakened immune systems.

Why Can Two People in the Same Home React Differently?

One person may experience significant symptoms while another person living in the same home feels completely well.

Individual responses can be influenced by:

• Asthma or existing allergies
• Chronic respiratory conditions
• Immune-system health
• Age and general health
• The amount and duration of exposure
• Differences in individual sensitivity

Children, people with severe asthma, those with chronic lung disease and people with weakened immune systems may be more susceptible to health effects.

This difference does not automatically prove or disprove that the building is contributing. It simply demonstrates that every body responds to environmental exposure differently.

Where Does Household Mould Come From?

Mould is fundamentally a moisture problem.

Common causes include:

• Roof, wall or plumbing leaks
• Blocked gutters and downpipes
• Flooding or previous water damage
• Condensation from showers and cooking
• Drying clothes indoors without ventilation
• Furniture positioned tightly against cold external walls
• Poor airflow in cupboards and closed rooms
• Persistently high indoor humidity

Even a relatively new home can develop mould if moisture is trapped inside or ventilation is inadequate. The age of a building alone does not determine whether it is protected.

Signs of a Possible Hidden Moisture Problem

Look beyond visible mould. Other warning signs may include:

• A persistent musty or earthy smell
• Bubbling, peeling or discoloured paint
• Water marks on walls or ceilings
• Warped timber or swollen skirting boards
• Regular condensation on windows
• Damp carpet or flooring
• Mould that returns soon after cleaning
• A room that consistently feels damp or poorly ventilated

If mould repeatedly returns, the underlying moisture source has probably not been resolved.

Should You Test Your Home for Mould?

Commercial mould testing is heavily promoted, but routine air sampling is not always necessary or useful.

The US Centers for Disease Control and Prevention does not recommend routine home mould testing. There are no universally accepted health-based indoor standards that can determine whether a particular test result will make someone ill.

A negative short-term air sample can also miss intermittent exposure or hidden moisture damage.

If mould can be seen or smelled, the practical priorities are generally to:

1. Find the source of the moisture.
2. Repair the leak, condensation or ventilation problem.
3. Remove the mould safely.
4. Dry the affected materials completely.
5. Replace porous materials that cannot be adequately cleaned.

Professional building assessment may be appropriate when the affected area is extensive, mould keeps returning, contamination is hidden, water damage has been severe or occupants are medically vulnerable.

Cleaning Mould Safely

Small areas on hard surfaces may sometimes be cleaned with household detergent or white vinegar, following government guidance and the product’s safety instructions.

Wear suitable gloves, eye protection and protective clothing. Ventilate the area and avoid spreading spores into unaffected rooms.

Never mix bleach with ammonia, acids, vinegar or other cleaning products. Mixing chemicals can release dangerous fumes.

Mould growing deeply inside porous materials such as carpet, ceiling tiles, insulation or plasterboard may be difficult to remove completely. These materials may need professional assessment or replacement.

People with severe asthma, allergies, chronic lung conditions or weakened immune systems should avoid personally cleaning significant mould contamination.

Prevention Begins With Moisture Control

Cleaning the surface without correcting the moisture problem is like silencing an alarm without putting out the fire.

To reduce the risk of mould:

• Repair leaks promptly.
• Use exhaust fans while showering and cooking.
• Ventilate rooms whenever outdoor conditions allow.
• Dry wet materials as quickly as possible.
• Avoid placing large furniture tightly against cold external walls.
• Address regular window condensation.
• Use a dehumidifier when appropriate.
• Keep gutters, downpipes and drainage systems maintained.

The US Environmental Protection Agency recommends drying water-damaged materials within approximately 24 to 48 hours whenever possible.

Listen to Your Body—Without Jumping to Conclusions

If symptoms consistently worsen inside a particular home, room or workplace and improve after leaving, that pattern is worth discussing with your doctor.

However, mould should not become the automatic explanation for every unexplained symptom. Fatigue, headaches, hormonal changes and brain fog may have numerous medical, psychological, environmental and lifestyle causes.

A responsible approach examines the whole picture:

• The person
• Their symptoms and medical history
• Their nervous-system state
• Their sleep and stress levels
• Their lifestyle
• The environment in which they spend their time

Healing is rarely about one isolated factor. Our bodies continuously respond to what is happening both within us and around us.

Sometimes, creating a healthier internal state begins with calming the nervous system. At other times, it also requires correcting something in the physical environment.

Your home should be a place where your body feels safe enough to rest, regulate and recover.

When to Seek Help

Speak with a healthcare professional if you develop persistent respiratory symptoms, unexplained health changes or symptoms that appear connected with a damp or mould-affected building.

Seek urgent medical assistance for severe breathing difficulty or another medical emergency.

References: NSW Health: Mould, WHO Guidelines for Indoor Air Quality: Dampness and Mould, Better Health Channel: Mould and Your Health, CDC: Mould and Health, and US EPA: Moisture and Mould Control.