Mold and your health

Mould is a type of fungus that lives on plant and animal matter. Indoors it can grow on:

• building materials such as wood and gypsum plasterboard
• furnishings such as carpet and curtains
• everyday items such as books and boxes

Mould grows best in damp, poorly ventilated areas, and it reproduces by making spores. Airborne mould spores are commonly found in both indoor and outdoor environments. When they land on damp spots indoors, they may begin to grow and spread.

There is no practical way to eliminate all mould indoors. The way to control indoor mould growth is to control the source of moisture, so it is important that your home has good ventilation to reduce internal moisture and prevent mould growing.

What mould looks like#

Mould is not always easy to recognise. It often looks like ‘fuzz’ or appears to be a stain, smudge or discolouration. The most common moulds are black, green or white, but mould can be many other colours, ranging from grey to orange to brown, and its colour can change depending on its age or life stage.

How mould affects health#

Mould associated with damp buildings can trigger nasal congestion, sneezing, cough, wheeze and respiratory infections, and can worsen asthma and allergic conditions.

People who are more likely to be affected by these symptoms and other serious health effects include those with:

• weakened immune systems
• allergies
• severe asthma
• chronic, obstructive or allergic lung disease

You should seek medical advice if you are concerned about the effects of mould.

Causes of mould growth indoors#

Mould only grows when there is enough moisture on a surface or humidity in the air. Common causes include:

• leaking roofs and walls
• faulty plumbing, including blocked gutters and downpipes
• condensation from cooking, showering and clothes drying, especially in areas with poor air circulation such as cupboards, corners, and furniture placed against uninsulated outside walls

Actions you can take to reduce mould#

The most important steps to prevent mould in your home are to:

• fix leaky plumbing, roofs and other building faults
• ensure gutters are cleared and maintained
• wipe up excess water caused by condensation, such as on single-glazed windows and shower glazing
• air the home regularly by opening windows and doors on warmer days
• use mechanical dehumidification or air conditioning if available

You can also reduce moisture and humidity in other ways:

• the cheapest and easiest way to reduce moisture is to ventilate a room by opening a door or window
• use exhaust fans, or open windows, in the bathroom and kitchen when showering, cooking or using the dishwasher
• vent clothes dryers to the outside and clean lint filters according to the manufacturer’s instructions
• if using evaporative cooling, ensure there are enough exhaust openings to the outside and follow the manufacturer’s instructions, as evaporative coolers add moisture to indoor air
• maintain and regularly service heating, ventilation and cooling systems according to the manufacturer’s instructions
• use a vacuum cleaner with a HEPA (high efficiency particulate air) filter
• avoid placing mattresses on the floor or on surfaces without adequate ventilation, and vacuum or turn mattresses if it can be done safely
• increase air circulation around furniture by moving it away from the walls

Rental properties with mould#

When a rental property has mould, the owner should fix any mould caused by faults such as gutters or other fixtures, while the tenant should make sure extractor fans are used where available and that the home is aired regularly where possible.

Sometimes the cause of mould growth is a building fault that cannot be easily fixed. If, as a tenant, you have taken steps to keep the building properly ventilated and mould is still growing, you should raise the issue with the owner.

Testing for mould#

Where mould is visible, it is generally not considered necessary to test for it in the home. However, not all mould is visible, as contamination may be in cavities or the ceiling. Generally, if you can see or smell mould, you should clean up and remove it promptly, as mould can damage the surfaces it grows on.

If you suspect mould contamination but cannot find the source, or if you have already taken steps to prevent mould and are still having problems, you could engage an occupational hygienist or environmental health and safety professional. For a fee, these professionals can provide specialist mould testing and consultancy services.

Key points#

• Airborne mould spores are commonly found in both indoor and outdoor environments.
• Good ventilation is important to reduce internal moisture and prevent mould growth.
• The most common moulds are black, green or white, but mould can be many other colours.
• People who are more susceptible to health effects include those with weakened immune systems, allergies, severe asthma or chronic lung disease.
• Sometimes the cause of mould growth is a building fault that cannot be easily fixed.

Where to get help#