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Mold vs mildew: how to tell the difference

Mildew and mold are both fungi, they both love damp surfaces, and in a humid place like West Palm Beach they both turn up constantly. The difference matters because one is usually a cleaning job and the other can signal a deeper moisture problem inside your walls, floors or HVAC system.

The quick answer

Mildew is a surface-level fungus. It grows flat, in grey, white or yellowish patches, on damp surfaces like shower grout, window sills and bathroom walls. It wipes away with household cleaner and tends not to come back if the surface dries out.

Mold grows into materials, not just on them. It appears fuzzy or slimy, in green, black, brown or orange, and it roots into porous materials like drywall, wood and carpet. Wiping the surface does not remove it - the growth continues underneath.

Telling them apart

Appearance

• Mildew: flat, powdery or downy texture. Starts white or grey, may turn yellow or brown. Sits on the surface.
• Mold: raised, fuzzy or slimy texture. Green, black, brown, orange or even pink. Often irregular spots that spread outward.

Smell

Both smell musty, but mold is stronger and more earthy - closer to rotting wood or wet soil. A persistent musty smell you cannot locate is one of the most reliable signs of hidden mold.

Location

Mildew stays on surfaces that get damp then dry - tile, grout, sills. Mold favours materials that stay damp: inside wall cavities after a leak, under carpet, in attic insulation, inside air conditioning ducts. If growth appears on drywall, skirting boards or ceilings, treat it as mold until proven otherwise.

The wipe test

Wipe a small patch with household cleaner while wearing gloves. If it comes away completely and the surface underneath is unmarked, it was probably mildew. If the surface is stained, soft or the growth returns within days, you are dealing with mold that has rooted into the material.

Why the difference matters in South Florida

West Palm Beach humidity sits between 72 and 75% for much of the year - above the level at which mold thrives. What starts as mildew on a bathroom wall can become a mold problem when moisture gets behind the surface through failed grout, a slow plumbing leak or condensation inside the wall cavity. Mold can take hold in as little as 48 hours after water intrusion.

When to handle it yourself - and when not to

Mildew and very small surface patches on non-porous materials are a DIY job. But for mold, Florida law requires a licensed professional for any growth over 10 square feet, and professional remediation is the only reliable approach for mold on porous materials, behind walls or in HVAC systems. Bleach does not fix it - it cannot reach the root structure inside porous materials, so the mold regrows.

For more on how professionals deal with confirmed mold, see our guide to mold removal services in West Palm Beach.