Mold vs mildew

What is the difference between mold and mildew?

Mildew is a kind of mold, not a different thing. The EPA says the term refers to certain kinds of mold or fungus and is often used generically for mold growth with a flat growth habit.¹ Molds, in the EPA’s definition, include all species of microscopic fungi that grow as multicellular filaments.¹

So when people say mildew, they usually mean thin surface growth in a damp spot. When they say mold, they usually mean growth that looks thicker, fuzzier or has gotten into the material underneath.

How can you tell them apart?

By where it is and how it sits on the surface, more than by color.

	Usually called mildew	Usually called mold
Texture	Flat, powdery or thin	Raised, fuzzy or slimy
Where	Shower walls, grout, windowsills, damp fabric	Drywall, wood, carpet, behind walls, under sinks
Depth	On the surface	Can grow into porous material
Wipes off?	Mostly, from hard surfaces	Often leaves a stain or returns

The EPA notes that mildew often lives on shower walls, windowsills and other places where moisture levels are high.¹ Color is a poor guide. Both can be gray, white, green or black, and the same mold can look different on different materials.

Is mildew less harmful than mold?

There’s no official health distinction. The CDC says all molds should be treated the same with respect to potential health risks and removal.³ California’s public health department says current scientific consensus doesn’t support singling out some molds as especially hazardous toxic molds, and that the evidence consistently tied to health effects is water damage, damp materials, visible mold and mold odor.⁴

What does differ is scale. A film of mildew on a windowsill is a small, visible problem. Growth inside a wall is a bigger, hidden one. For health questions, talk to your doctor.

How do you clean mildew and surface mold?

On hard surfaces, the EPA’s method is simple: scrub with detergent and water, then dry completely.²

• Wear gloves, and avoid touching mold with bare hands.²
• Skip bleach as a routine step. The EPA doesn’t recommend biocides like chlorine bleach as routine practice, and warns never to mix bleach with cleaners containing ammonia.²
• Don’t paint or caulk over it. The EPA says to clean and dry the surface first, because paint applied over mold is likely to peel.²
• Then fix the moisture. Mold cleaned up without fixing the water problem will most likely come back.²

Porous materials such as ceiling tiles and carpet may have to be thrown away if they become moldy, because mold can grow into them and be difficult or impossible to remove completely.² For the bathroom specifically, see black mold in the shower.

When is it more than mildew?

Treat it as a bigger problem when:

• It returns within weeks of cleaning, even with good ventilation
• It’s on drywall, wood or carpet rather than tile, glass or sealed surfaces
• It covers more than about 10 square feet, the EPA’s threshold for when most people can clean it themselves²
• It sits near a pipe, window or exterior wall that might be leaking
• It shows up on clothes, shoes or bags stored in a closet
• It comes with a musty smell that lingers after cleaning

Mildew on stored clothing deserves a second look. The EPA notes that molds can thrive on clothing, leather and paper in homes with moisture problems.¹ Washing the items fixes the items, not the closet. Check whether the closet sits on an exterior wall, whether the wall feels cold or damp, and whether the door stays shut most of the day.

When should you call an inspector?

Most mildew doesn’t need one. A film on a shower wall or a windowsill with a known cause is a cleaning job, and recurring windowsill growth usually points to condensation on the windows.

Call when the growth matches the list above or you can’t tell what you’re looking at. Send us a photo first if you’re unsure. A mold inspection is $495 for one dwelling up to 2,000 sq ft, and an optional surface sample at $125 can identify a stain that might not be mold at all.