Quick answer: A musty smell, stains that keep returning, peeling paint, soft drywall, condensation that won’t clear, and health symptoms that ease when you leave the house are the most common signs of mould.
Smell firstA musty, earthy smell that won’t clear is one of the best early signs.
Look in the cornersWindow frames, under sinks, around caulking and along exterior walls.
Watch the paintBubbling, peeling or stains that come back point to moisture behind the surface.
Feel the materialsSoft drywall, spongy wood and lifting floors mean moisture has been there a while.
How many signs are you seeing right now?

1 or 2 ticked: Keep an eye on it and fix the moisture. 3 or more: book a free consult so we can find the source.

Where to look, room by room

Basement

Check the bottom of the walls, floor corners, stored boxes and the area around the floor drain. Musty smell and white or grey fuzz are common here.

Bathroom

Look at the ceiling, grout, caulking around the tub and behind the toilet. Dark spots that return after cleaning are the usual sign.

Kitchen

Check under the sink, the back of cabinets and the area around the dishwasher. Slow leaks often hide here.

Bedroom closets and exterior walls

Furniture against cold exterior walls and closets with no airflow are common spots, especially in winter.

What each sign usually means

Sign What it usually means Next step
Musty smell that stays Moisture or mould somewhere out of sight Find the damp area with your nose and a torch
Stain that returns after painting Moisture is still active behind the surface Find the source before you paint again
Soft drywall or spongy wood Moisture has been there long enough to affect the material Get a professional assessment
Condensation that won’t clear Humidity or poor airflow Ventilate, lower humidity and check the windows
Rain on a window, the same kind of cold surface where condensation builds up.
Rain on a window, the same kind of cold surface where condensation builds up.

Feel and sound: the signs you can’t see

Drywall that feels soft or crumbles, wood that feels spongy, and floors that bounce or lift can mean moisture has been there long enough to affect the structure, not just the surface. Press gently on suspect areas and listen for a dull sound.

Health symptoms to watch for

Some people notice sneezing, congestion, itchy eyes, headaches or coughing that eases when they leave the house. Symptoms like these are worth raising with a doctor, especially if they keep coming back.

What to do if you spot these signs: find the moisture source before you clean, avoid disturbing large areas of mould without protection, and get a professional assessment if the growth is larger than a small patch.

Frequently asked questions

Is a musty smell always mould?

Not always, but it is one of the most common signs of hidden mould. If the smell persists after cleaning and ventilating, have the area checked.

Does the colour of mould tell me if it’s dangerous?

No. Colour does not tell you the type of mould. Testing is the only reliable way to identify it.

When should I get a professional to look?

If the growth is larger than a small patch, is behind walls or under floors, keeps returning, or if anyone in the home has ongoing symptoms.

Can I check for mould myself?

You can look for the signs in this article. Finding the source of moisture is the most useful first step. For hidden mould, a professional inspection is the reliable way to know.

Related searches: signs of mould in house, how to tell if you have mould, musty smell mould, mould symptoms, black mould signs, hidden mould signs

If you want a professional look at your home, see our mould remediation service or inspection and testing.

Keep plugging in: what to read next

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    This guide relates to our Mould Remediation service. Book a free site visit.

    When to get a professional look

    Visible mould across a large area, mould that returns after cleaning, mould behind walls or under flooring, and any musty smell with no visible source all justify a professional assessment. A written report at the start gives you a baseline to check the work against at handover.

    Ask for the photos and the written record at handover. A clear record tells you what was found, what was done and what still needs watching.