Mildew is a common term for certain kinds of mould or fungus, particularly flat growth on surfaces. The label does not determine the seriousness or the treatment. Whether you need professional help depends on the extent of growth, the material affected, whether it returns after cleaning, and whether the moisture source has been addressed.
What mould and mildew mean
The US EPA explains that mildew is a term commonly used for certain kinds of mould or fungus, particularly flat growth on surfaces. It is not a scientifically separate category from mould. Both are fungi that grow where there is moisture and organic material.
In everyday use, people often call flat, powdery growth "mildew" and raised, fuzzy growth "mould", but this distinction does not reliably tell you the species, how deep it goes, or how serious it is. The label does not determine the treatment.
Why the label does not determine the treatment
Whether you call visible growth mould or mildew, the practical questions are the same:
- What material is it on? Growth on non-porous surfaces (tiles, glass, laminate) is generally easier to clean. Growth on porous materials (drywall, wood, grout, fabric) may be harder to remove because fungal filaments (hyphae) can penetrate the material.
- How much is there? A small patch on a tile is different from a large area across a wall or ceiling.
- Does it come back after cleaning? Recurrence after cleaning may point to an unresolved moisture source or incomplete removal, regardless of what you call the growth.
- What is the moisture source? Condensation, a leak, poor ventilation or rising damp. Without addressing the moisture, growth is likely to return.
The EPA's cleanup guide says the approach is the same regardless of what type of mould is present: fix the water problem, dry the area, clean or remove affected material.
When you can clean it yourself
Small patches of growth on hard, non-porous surfaces can often be cleaned with a household mould-removal product and improved ventilation. The bleach and mould spray guide explains what cleaning products can and cannot do.
When to arrange a professional assessment
Consider professional assessment when:
- Growth covers a large area (roughly one square metre or more).
- Growth is on porous materials and cleaning has not resolved it.
- Growth returns after cleaning, which may indicate the moisture source is unresolved or the material needs replacement.
- There is a musty smell without visible growth, suggesting hidden mould.
- You are unsure of the moisture source or cannot access the affected area.
These criteria apply regardless of whether you call the growth mould or mildew. The bathroom mould guide covers treatment for grout, silicone and ceilings. The condensation-or-leak guide helps identify the moisture source.
What to observe and photograph before paying for anything
- Where exactly is the growth? Note the room, wall, height and proximity to water sources.
- What surface is it on? Tile, painted wall, drywall, wood, grout, silicone, fabric.
- Is the area damp or dry? Check for condensation, water stains or an active leak.
- Has it been cleaned before? If so, how long before it returned?
- Is there a musty smell in areas without visible growth?
Share these observations with the assessor. They help determine whether the issue is surface cleaning, material replacement, or moisture remediation.
Four Solutions assesses the moisture source alongside the visible growth to determine the right scope. The mould inspection guide explains what an assessment covers.
Frequently asked questions
Is mildew a different thing from mould?
The US EPA explains that mildew is a term commonly used for certain kinds of mould or fungus, particularly flat growth on surfaces. It is not a scientifically separate category. Both are fungi that need moisture to grow.
Can I tell what I have by the colour?
Not reliably. Mould and mildew appear in many colours. Colour alone does not tell you the species, whether it is active, or how serious it is. What matters for treatment is the material affected, the extent of growth and whether the moisture source is resolved.
When does fungal growth need professional treatment?
Consider professional assessment when growth covers a large area, affects porous materials (drywall, wood, grout), returns after cleaning, or when there is a musty smell without visible growth. The deciding factors are extent, material and moisture source, not whether you call it mould or mildew.
Should I test before cleaning?
The EPA notes that where visible mould growth is present, sampling is generally not needed to decide that cleanup is necessary. The basic response is the same: address the moisture source, clean or remove affected material, and dry the area. Testing can answer other questions (species identification, clearance verification, insurance or dispute documentation) but should have a defined purpose before you pay for it.
Arrange a mould assessment
Ask Four Solutions about your mould or mildew
Sources: US EPA: what is the difference between mold and mildew. EPA mold cleanup in your home. EPA brief guide to mold, moisture and your home. Guidance checked 18 October 2026.