Mould identification key

Answer whatever you can — every question is optional. Texture is asked before colour, deliberately: colour is the least reliable property mould has, and it is what almost everyone leads with.

The species matters less than you think

Public health guidance is to remove all indoor mould regardless of type. The CDC and EPA do not recommend routine species testing for ordinary households, because the response does not change: find the water, stop it, remove the growth.
“Toxic black mould” is a marketing phrase, not a category. Stachybotrys is real and does need soaked material to grow, so finding it tells you something useful about your building. But the health effects that are well established — allergy, asthma aggravation, irritation — are not specific to it.
Mould without water does not persist. Cleaning growth while leaving the moisture source is why it comes back. The leak, the condensation or the ventilation is the actual problem.

Call a professional for areas larger than about 10 square feet, for anything in HVAC ductwork, after sewage or flood water, or if anyone in the household is immunocompromised or has a lung condition.

1.Where is it?

optional

Location narrows things faster than appearance, because each part of a house has its own moisture problem and its own usual suspects.

2.What does it feel and look like?

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Texture is far more diagnostic than colour. Slimy, powdery and crusty point in three completely different directions — and crusty usually means it is not mould at all.

3.What is it growing on?

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Material matters. Nothing grows on bare masonry that also grows on bread, and a white crust on concrete is almost certainly a mineral deposit.

4.What colour is it?

optional

Last, and deliberately so. Dozens of unrelated moulds are black, and colour changes as a colony matures — it is the least reliable thing about mould and the thing people lead with.

11 possibilities

Answer any question to begin

3 of these are not mould at all