A dark spot in the shower and a dark stain spreading across drywall can look alike at first glance. One is often surface mildew you can wipe away; the other may be mold growing into a building material that has stayed wet. Here is how to tell them apart, and when it is time for a closer look.
What Is Mildew?
“Mildew” is the everyday name for mold growth that stays flat on a surface. It tends to look powdery or downy and is usually white, gray or yellowish, sometimes darkening over time. You will find it on damp, hard surfaces — shower grout, window sills, bathroom ceilings — and on fabrics that stayed damp. On hard surfaces it usually cleans off easily.
What People Mean by “Black Mold”
“Black mold” usually refers to Stachybotrys chartarum, a greenish-black mold that grows on materials rich in cellulose — the paper facing of drywall, wood, ceiling tiles — when they stay wet for a long time. It is often found behind walls or under flooring after a leak.
But many common molds are dark green, gray or black, so a dark color on its own does not mean you have Stachybotrys.
How to Tell Them Apart
- Appearance: Mildew is flat and powdery. Mold is often fuzzy or slimy, raised, and may spread in irregular patches.
- Where it grows: Mildew sits on the surface of tile, glass and sealed finishes. Mold grows into porous materials such as drywall, wood and insulation.
- After cleaning: Mildew wipes away and stays away longer when the area is kept dry. Mold that has grown into a material leaves staining and returns quickly.
- Smell: Both can smell musty, but a strong, persistent odor with little visible growth can point to a larger hidden problem.
Color Cannot Identify the Species
Only laboratory analysis can identify a mold species, and for most homeowners it is not necessary. The CDC advises that all molds be treated the same way with respect to health risks and removal. What matters is how much growth there is, what it is growing on, and the moisture that allowed it to grow.
When You Can Clean It Yourself
The EPA suggests homeowners can usually handle areas of roughly 10 square feet or less. For small spots on hard surfaces:
- Wear gloves, eye protection and an N-95 respirator
- Scrub with detergent and water, then dry the surface completely
- Never mix bleach with ammonia or other cleaners
- Fix the moisture source — a leak, poor ventilation or condensation — so it does not come back
When to Call a Professional
Call for help when the area is larger than about 10 square feet, when mold has grown into drywall, insulation or carpet, when it keeps returning, when it follows water damage, or when you smell mold but cannot find it. Professional black mold removal services address the growth and the conditions behind it, and mold testing can help when the situation is unclear.