How to Identify Different Types of Mould in Your Home

Not all mould is the same. While most people have heard of "black mould," there are actually hundreds of mould species that can grow indoors. Each has different characteristics, preferred environments, and health implications. Understanding what you're dealing with helps you respond appropriately — and know when professional help is essential.

Here's a practical guide to the most common types of mould found in Australian homes.

Black mould (Stachybotrys chartarum)

This is the one that gets the most attention, and for good reason. Stachybotrys chartarum — commonly called toxic black mould — is a particularly concerning species.

What it looks like

Stachybotrys is typically dark black or dark greenish-black with a slimy or wet appearance when actively growing. When it dries out, it can appear powdery. It usually grows in thick, irregular patches rather than thin films.

Where it grows

Stachybotrys needs consistently high moisture and cellulose-rich materials to thrive. Common locations include:

• Water-damaged plasterboard — particularly behind walls or above ceiling tiles
• Chronically damp timber — subfloor framing, roof trusses with leaks
• Flood-affected materials — carpet backing, underlay, particle board
• Paper products — stored boxes, books, and documents in damp areas

It doesn't typically grow on tiles or glass. If you see dark mould on your bathroom tiles, it's more likely Cladosporium or Aspergillus.

Health risks

Stachybotrys produces mycotoxins — toxic compounds that can cause serious health effects with prolonged exposure. Symptoms may include persistent coughing, difficulty breathing, chronic fatigue, headaches, and in severe cases, neurological effects. It's particularly dangerous for children, the elderly, and immunocompromised individuals.

If you suspect Stachybotrys, do not attempt to remove it yourself. Professional remediation with proper containment is essential.

Aspergillus

Aspergillus is one of the most common indoor mould genera, with over 180 known species. It's found in virtually every home to some degree — the concern is when it grows in visible colonies.

What it looks like

Aspergillus colonies vary widely by species. They can be green, yellow, white, brown, or black. The texture is usually powdery or velvety. Some species form distinctive circular colonies that spread outward.

Where it grows

Aspergillus is versatile and can colonise a wide range of materials:

• Bathroom walls and ceilings — particularly in poorly ventilated spaces
• Air conditioning systems and ductwork — it thrives in the condensation inside HVAC systems
• Food — it's the mould you often see on bread, fruit, and other organic matter
• Dust — Aspergillus spores are a significant component of household dust

Health risks

Most Aspergillus species are relatively harmless to healthy individuals. However, certain species — particularly Aspergillus fumigatus and Aspergillus niger — can cause aspergillosis, a range of respiratory conditions from mild allergic reactions to invasive lung infections. People with asthma or weakened immune systems are at significantly higher risk.

Cladosporium

Cladosporium is another extremely common mould — often the most prevalent airborne mould species in outdoor and indoor environments across Australia.

What it looks like

Cladosporium typically appears as olive-green to brown or black spots or patches. It has a suede-like or powdery texture and often grows in clusters of small spots rather than large uniform patches.

Where it grows

Cladosporium prefers cool to moderate temperatures, which makes it particularly common during Sydney's cooler months:

• Window frames and sills — especially where condensation forms
• Bathroom ceilings and grout — the classic "spotty" mould pattern
• Exterior surfaces — it frequently grows on external timber, painted surfaces, and shade cloth
• Fabrics and carpets — particularly in damp rooms or near leaks
• Inside wardrobes — against exterior walls with poor airflow

Health risks

Cladosporium is generally considered a lower-risk species, but it's a significant allergen. Prolonged exposure can trigger hay fever symptoms, asthma attacks, and skin irritation. Because it produces vast quantities of airborne spores, it can significantly affect indoor air quality even in relatively small colonies.

Penicillium

Yes, this is the genus that gave us penicillin — but the species that grow in your home aren't doing you any pharmaceutical favours.

What it looks like

Penicillium is typically blue-green or blue-grey with a velvety or powdery texture. It's the classic "blue cheese" mould appearance. Colonies often have a white border at the growing edge.

Where it grows

Penicillium is a fast coloniser that spreads quickly on:

• Food — it's the most common mould on stored food
• Wallpaper and paint — particularly in damp bedrooms and living areas
• Carpet and underlay — especially after water damage
• Mattresses and upholstered furniture — in humid environments
• Insulation materials — fibreglass and foam

Health risks

Penicillium species are potent allergens and some produce mycotoxins. Chronic exposure can cause respiratory symptoms, sinus infections, and hypersensitivity pneumonitis — a condition where the lungs become inflamed from breathing in mould spores. It's a particular concern in bedrooms where exposure is prolonged during sleep.

Why visual identification isn't enough

While knowing what to look for is useful for an initial assessment, visual identification alone cannot reliably determine the exact mould species. Many species look similar, and multiple species often grow together. Colour can also change depending on the growth stage, moisture level, and substrate.

The only reliable way to identify mould species is through laboratory testing — either air quality sampling or surface swab analysis. Professional mould testing tells you exactly what you're dealing with, how concentrated the spores are, and what treatment approach is appropriate.

What to do if you find mould

Regardless of the type, any visible mould growth in your home indicates a moisture problem that needs addressing. Small patches on hard surfaces can be cleaned with vinegar. Anything larger than one square metre, anything on porous materials, or anything you suspect might be Stachybotrys should be handled by a professional.

At Pureairo, our treatment approach uses SAN-AIR technology — independently tested by UNSW and Eurofins — to eliminate mould without harsh chemicals. We don't just treat the surface; we address the root cause and provide ongoing protection against regrowth.

If you're unsure what type of mould you're dealing with, contact us for a free assessment. We'll identify the problem, test if needed, and recommend the right course of action for your situation.