What’s the difference between mold and mildew?

The full picture

Both mold and mildew are fungi. They both need moisture, an organic food source, and time. The differences are in how deeply they have rooted into the material and how disruptive they are to remove. Here is how a homeowner can read the signs.

Mildew — the surface fungus

• Appearance: flat or powdery; usually white, gray, or pale yellow.
• Texture: sits on top of the surface. Wipes off with a damp cloth, often leaving a clean spot.
• Common locations: high-humidity surfaces — bathroom grout, window sills, basement walls, stored items.
• Smell: faint, dry, slightly musty.
• Typical resolution: address the humidity (often with a dehumidifier or improved ventilation), then clean. Range: often in the low hundreds for materials and labor.

Mold — the deeper fungus

• Appearance: fuzzy, slimy, or raised; colors include black, green, brown, dark gray, sometimes orange or pink.
• Texture: grows into the substrate. Wiping the surface clears the top but the colony is still rooted.
• Common locations: drywall back-paper, wood framing, carpet padding, insulation, anywhere with sustained moisture and organic material.
• Smell: stronger, persistent, often described as “musty” or “earthy.”
• Typical resolution: source control (stop the moisture), containment during removal, replacement of affected porous materials, HEPA-grade air cleaning. Range varies significantly by scope and area; small contained jobs are often in the low thousands, while extensive remediation can reach the low five-figures.

The “is it mold or mildew?” home test

1. Look at the depth. Take a damp cloth and wipe a small patch. If the surface comes clean and the material underneath looks normal, that points to mildew. If staining or fuzzy material remains in the material, treat it as mold until proven otherwise.
2. Check the smell. A faint dry odor is more consistent with mildew. A persistent musty smell that lingers after the area is dry is more consistent with mold.
3. Look at the material. Mildew on a non-porous surface (tile, painted concrete) is typically easy to manage. Anything on drywall, wood, paper, or carpet padding deserves a closer look.

A note on health claims

Reactions to mold and mildew vary by person and by exposure. We do not make health diagnoses. If household members have symptoms that line up with a damp basement or visible growth, consult a physician. From a building-science standpoint, our job is to identify the source, contain the colony, and restore the space to a dry, stable condition.

When to call

If you see growth on porous materials, smell something persistent, or have a visible patch larger than roughly 10 square feet, schedule a free inspection. We will identify which fungus we are dealing with and write the scope before any work is quoted.