Mold vs Mildew: How to Tell the Difference in Your UK Home

The words "mold" and "mildew" are often used interchangeably in everyday conversation — but they describe different types of fungi with distinct appearances, behaviours, and treatment needs. Understanding the difference helps you respond appropriately, rather than over- or under-treating a fungal growth problem in your home.

What is Mildew?

Mildew is a surface-growing fungus that typically appears as flat, white, grey, or yellowish patches with a powdery or fluffy texture. It grows on the surface of materials rather than penetrating into them, which is why it is generally easier to treat than mold. Mildew is commonly found on:

• Shower curtains and bath sealant
• Bathroom tiles and grout
• Window frames and sills where condensation collects
• Damp clothing or stored fabrics
• Plant leaves (powdery mildew is a common plant disease)

Mildew does produce a musty odour, but it is generally milder than the pungent smell associated with mold.

What is Mold?

Mold is a multi-cellular fungus that grows in raised, fuzzy or slimy colonies in shades of green, black, blue, orange, or brown. Unlike mildew, mold penetrates into porous materials — it sends rootlike structures (hyphae) deep into plaster, timber, fabric, and paper, making it significantly harder to remove from the surface. Common UK household molds include:

• Cladosporium: Olive-green to black patches, very common, usually superficial on walls
• Aspergillus: Various colours including white, green, or yellow. Can cause allergic reactions and, in immunocompromised individuals, serious respiratory infection.
• Penicillium: Blue-green, velvety appearance. Frequently found on water-damaged building materials.
• Stachybotrys chartarum: The notorious black mold. Slimy texture, grows on cellulose-rich materials after prolonged moisture exposure. Produces mycotoxins.

How to Tell Them Apart

Characteristic	Mildew	Mold
Colour	White, grey, yellow	Black, green, blue, orange
Texture	Flat, powdery, fluffy	Raised, fuzzy or slimy
Penetration	Surface only	Penetrates into materials
Smell	Mild, musty	Strong, pungent, earthy
Treatment	Surface cleaning	May require material removal
Health risk	Mild irritant	Significant; varies by species

Treatment Approaches

Treating Mildew

Surface mildew on hard surfaces can typically be removed with a proprietary antifungal spray or a white vinegar solution, firm scrubbing, and thorough drying. Always address the underlying moisture — usually condensation from inadequate ventilation — or the mildew will quickly return. Antifungal paint and sealants help prevent regrowth on bathroom surfaces.

Treating Mold

Surface mold on non-porous materials can be treated similarly to mildew for small areas. However, mold on porous materials (plasterboard, timber, carpet) cannot be effectively treated by surface cleaning — the fungal hyphae penetrate deep into the material. Professional assessment is recommended for mold on porous surfaces, for areas exceeding 1m², or for any dark mold that could be Stachybotrys.

If you are unsure whether you have mildew or mold — or if the problem is recurring despite treatment — call Flash Restorations on 0800 123 4567 for a professional assessment and identification.