What does black mold look like?
Last updated: 2026-06-18
"Black mold" is the name homeowners give to dark mold growth they find on a damp wall, ceiling, or baseboard — most often the species Stachybotrys chartarum, though several ordinary molds look similar. You usually can't identify the exact species by eye, but you can learn to recognize what mold looks like versus a harmless stain, and that's enough to know whether you have a moisture problem worth acting on. Here's what to look for.
Color
Despite the name, "black" mold is rarely a pure, even black. Active growth is typically a dark green-black, greenish-gray, or charcoal color, sometimes with a faint olive or brownish tint at the edges. As a patch dries out it can look more flat black and sooty. Be careful with color alone, though: mildew and many household molds also show up as black or gray speckling, and not everything dark is mold at all (see "what gets mistaken for it" below).
Texture
Texture is one of the more telling clues. When Stachybotrys is actively growing on a wet surface it often looks slimy, wet, or slightly shiny, almost like a smear of dark paint or grease. As it dries it becomes powdery and soot-like, and can smudge or release dust if disturbed. Other molds look fuzzy, cottony, or velvety rather than slimy. Any of these textures — slimy, powdery, or fuzzy — points to mold rather than a stain.
Pattern and where it grows
Mold grows outward from a moisture source, so it tends to form circular, blotchy, or irregular spreading patches rather than the straight lines or uniform discoloration you'd get from water staining or dirt. Look for it where moisture collects:
- Bathroom walls, ceilings, grout, and around tubs and showers
- Under and behind sinks, dishwashers, and washing machines
- Basement and crawl-space corners, and the bottom edge of drywall
- Around windows with condensation, and on ceilings under a roof leak
- On wood framing, paper-faced drywall, ceiling tiles, and cardboard — mold loves these cellulose-rich materials
Smell
Mold often announces itself before you see it. A persistent musty, earthy, "old basement" odor — strongest in one area, or worse after rain or when the HVAC runs — is a classic sign of active growth, sometimes hidden inside a wall or above a ceiling. If you can smell mold but can't find it, treat the smell as real evidence and keep looking (or have it inspected).
What gets mistaken for black mold
Plenty of dark marks aren't mold. Before you panic, rule out the look-alikes:
- Dirt, soot, and grime — wipe a small area with a damp cloth. Dirt comes off cleanly and stays gone; mold smears, may smell musty, and grows back.
- Mildew — a surface mold that's usually gray/white and powdery, easier to clean, and stays on the surface rather than rooting into the material.
- Water stains — brown or yellowish rings with no texture and no smell; a sign of past moisture, not necessarily active mold (though they tell you to check for it).
- Efflorescence — white or grayish mineral salts that crystallize on concrete and brick basements. It's crusty and dissolves in water; mold doesn't.
The reliable tell: mold is tied to moisture and it comes back. If a dark patch is in a damp area, has a musty smell, smears or feels slimy/fuzzy, or returns after cleaning, treat it as mold.
Color can't confirm the species — only testing can
It's worth being clear: you cannot tell Stachybotrys from other dark molds by looking, and even a lab ID doesn't change the basic homeowner playbook. What matters is that visible mold means you have excess moisture, and growth on porous materials needs to be removed properly so it doesn't spread or return. If you want the species identified — or you suspect hidden growth — that's what a mold inspection is for. For more on telling whether you have a mold problem at all, see signs of mold in your house, and for the health angle, is black mold dangerous?
When to call a pro
A small patch of surface mold (under roughly 10 square feet) on a hard, non-porous surface can often be cleaned by a homeowner. Call a professional when the area is larger, when mold is on or behind porous materials like drywall or insulation, when it keeps coming back, when you smell mold but can't find it, or when it followed a flood or sewage backup. A remediation pro will contain the area, remove affected materials safely, and — most importantly — fix the moisture source so it doesn't return. Connect with a vetted local mold remediation pro to get matched.
Frequently asked questions
- The mold people call "black mold" (often Stachybotrys chartarum) usually appears as dark green-black or charcoal patches with a slimy or wet, slightly shiny surface when it's actively growing, drying to a soot-like, powdery texture. It tends to grow in circular or irregular spreading patches on damp, cellulose-rich materials like drywall, ceiling tile, and wood, and it often comes with a strong musty, earthy odor.
- Dirt and soot wipe away cleanly and don't come back; mold smears, may feel slimy or fuzzy, often has a musty smell, and returns even after you clean the surface because its roots (hyphae) are in the material. Mold also tends to appear where there is or was moisture — under a leak, around a tub, in a damp basement corner — rather than in a random clean, dry spot.
- No. Many common molds look dark and are not Stachybotrys, and even Stachybotrys is better described as an indoor-air and water-damage problem than a guaranteed "toxic" one. Color alone can't confirm the species — only lab testing can. From a homeowner's standpoint the species matters less than the fact that visible mold plus moisture means you have a moisture problem to fix and growth to remove.
- Yes — and that's common. Mold frequently grows inside wall cavities, under flooring, above ceiling tiles, and around HVAC systems, where a persistent musty smell may be the only clue. If you smell mold but can't find it, or you've had a leak or flood, a professional inspection can find hidden growth before you open up the wall.