Mold vs. Mildew: How to Tell the Difference

Homeowners often use “mold” and “mildew” interchangeably, but they’re different organisms that require different responses. Knowing which you’re dealing with affects how you address it — and whether you need professional help.

What Is Mildew?

Mildew is a surface fungus that grows on moist surfaces — typically flat and powdery in appearance, usually white, grey, or yellow. It tends to stay at the surface and doesn’t penetrate into the material it’s growing on.

Common locations:

• Shower tiles and grout
• Window sills with condensation
• Fabric left damp (shower curtains, towels)
• Plant leaves

Mildew typically responds well to cleaning with over-the-counter products. It doesn’t usually penetrate into materials, so surface treatment is often sufficient.

What Is Mold?

Mold is also a fungus, but it’s more complex and potentially more problematic. Mold comes in thousands of species and can appear in many colours — black, green, blue, white, orange, red. Unlike mildew, mold can penetrate into porous materials like drywall, wood, and insulation.

Key differences from mildew:

• Often fuzzy or raised in texture (rather than flat/powdery)
• Can be multiple colours — not just white/grey
• Penetrates into the material, not just on the surface
• More likely to cause structural damage if left untreated
• More likely to cause health effects, particularly in sensitive individuals

How to Tell Them Apart

Appearance:

• Mildew: flat, powdery, white/grey/yellow
• Mold: fuzzy, raised, can be black/green/blue/white

Response to cleaning:

• Mildew: cleans off easily with standard bathroom cleaner
• Mold: may appear to clean off the surface but returns — the colony is inside the material

Smell:

• Both can produce a musty odour, but mold tends to be more pungent

Location:

• Mildew: typically stays in high-humidity surface areas (shower, windowsill)
• Mold: can grow anywhere there’s moisture, including inside walls, under floors, and in attics

When to Call a Professional

Mildew: You can typically handle surface mildew yourself with appropriate cleaning products, good ventilation, and addressing the source of humidity.

Mold: Call a professional when:

• The affected area is larger than 10 square feet (roughly 3’ × 3’)
• You can smell mold but can’t locate it visually
• Mold returns quickly after surface cleaning
• You suspect mold is inside a wall, under flooring, or in your attic
• Anyone in the household has respiratory conditions or immune system concerns

If you’re not sure which you’re dealing with, contact us for a free assessment — we can identify the type of growth and recommend the appropriate response.