5 Signs You Have Toxic Mould in Your Home

Mould isn't just unsightly — certain species produce mycotoxins that can cause serious health problems. While the term "toxic mould" is sometimes overused, the health risks of prolonged exposure to indoor mould are well documented. Here are five signs your home may have a mould problem that needs attention.

1. A persistent musty smell

The most reliable early warning sign is smell. Mould produces microbial volatile organic compounds (MVOCs) as it grows — these create that distinctive musty, earthy odour.

Key point: If you can smell mould, it's there — even if you can't see it. Mould often grows inside wall cavities, under flooring, behind cabinets, and in ceiling spaces where it's completely hidden from view.

Don't ignore the smell or try to mask it with air fresheners. If a room smells damp or musty, investigate.

2. Unexplained health symptoms

Mould exposure affects people differently. Some are highly sensitive, while others show no symptoms at all. Common signs include:

• Respiratory issues — persistent coughing, wheezing, shortness of breath
• Allergic reactions — sneezing, runny nose, itchy or watery eyes
• Skin irritation — rashes, itching, or dermatitis
• Headaches and fatigue — chronic tiredness that doesn't improve with rest
• Difficulty concentrating — brain fog, especially in affected rooms

The telltale clue: Symptoms improve when you leave the house and worsen when you return. If your "cold" goes away on holiday and comes back when you get home, mould could be the cause.

Children, elderly people, asthmatics, and immunocompromised individuals are most at risk. Pets are also vulnerable — read our guide on mould and pet safety.

3. Visible mould growth

This sounds obvious, but mould isn't always the dramatic black patches you see in photos. Early-stage mould can appear as:

• Small dark spots that look like dirt or soot
• White or grey fuzzy patches on walls or ceilings
• Green, yellow, or pink discolouration on grout or silicone
• Dark streaks around window frames or air conditioning vents

Check these common hiding spots:

• Behind and under furniture against exterior walls
• Inside wardrobes and cupboards
• Under sinks and around pipe penetrations
• Ceiling corners, especially in bathrooms and laundries
• Window sills and tracks
• Behind refrigerators and washing machines

4. Water damage or moisture problems

Where there's moisture, there's mould — usually within 24 to 48 hours. Signs of moisture problems include:

• Water stains on ceilings or walls (brown or yellow rings)
• Bubbling, peeling, or cracking paint
• Warped or buckled flooring
• Condensation regularly forming on windows
• Damp patches that come and go on walls
• Rising damp — tide marks along skirting boards

Even if you've fixed a leak, the mould may already be established in the affected materials. Plasterboard, timber framing, and carpet underlay can harbour mould growth long after the visible water is gone.

5. Your home was built or renovated during a wet period

Homes built or renovated during prolonged wet weather are at higher risk. If building materials got wet during construction and weren't properly dried before being enclosed, mould can establish itself inside wall cavities from day one.

This is particularly common in:

• Homes built during La Nina years
• Properties that sat unroofed during rain
• Renovations where wet trades (plastering, painting) were rushed
• Buildings with inadequate ventilation design

What to do if you suspect toxic mould

Step 1: Don't disturb it. Scrubbing or pulling away materials without containment spreads spores throughout the home, making the problem worse.

Step 2: Get professional testing. Air sampling and swab testing identify the species present and the concentration of spores. This tells you exactly what you're dealing with and how serious it is.

Step 3: Address the moisture source. No remediation will last if the moisture problem isn't fixed. This might mean repairing leaks, improving ventilation, or installing extraction systems.

Step 4: Professional remediation. For anything beyond a small surface patch, professional treatment ensures the mould is fully eliminated — not just painted over. At Pureairo, we use SAN-AIR technology — including air purification — a 100% natural plant-based treatment that kills mould without harsh chemicals, making it safe for families with children and pets.

The bottom line

Mould in your home isn't normal, and it shouldn't be ignored. If you're seeing any of these signs — especially the health symptoms — take action early. The longer mould grows, the more expensive and disruptive the remediation becomes.

A professional assessment takes less than an hour and gives you a clear picture of what's happening in your home. We offer free initial assessments across Sydney and our service areas. Wondering about cost? See our guide to mould remediation costs in Australia.