Black mold, the common name for Stachybotrys chartarum, is a greenish-black mold that grows on building materials that stay wet. It often looks slimy while it is growing and darker and sootier once the surface dries. But plenty of other molds are dark, and plenty of dark stains are not mold at all, so appearance is only a starting point.
This guide describes what black mold usually looks like, what it is often confused with, and what to do if you think you have found it. For background on what black mold is and why it grows, see our black mold guide.
What black mold usually looks like
Signs that point toward Stachybotrys:
- Color: greenish-black to black, sometimes with gray or dark green edges
- Texture: wet, slimy, or tar-like on damp material; flatter and sootier as it dries
- Shape: spots that merge into irregular patches and spread outward from the wettest area
- Material: growing on the paper face of drywall, ceiling tiles, wood, cardboard, or paper, which are the cellulose-based materials the CDC describes it favoring
- Setting: near a water source, such as below a roof leak, behind a sink or toilet, around a leaking window, or low on walls after a flood
- Company: water stains, bubbling or peeling paint, soft or crumbling drywall, and a musty smell
The last two points matter more than color. Stachybotrys needs constant moisture, so it almost always appears where a material has been wet for days or weeks.
Other dark molds that look similar
Several molds commonly found indoors are dark green, brown, or black. They can grow on bathroom surfaces, window frames, air conditioning vents, and damp walls, and to the eye they can look much like Stachybotrys. The EPA's own training materials remind readers that mold comes in many colors, not just black.
This is why "black mold" pictures online can mislead. A photo can show you what a dark mold looks like; it cannot tell you which species is on your wall.
Black spots in the shower
The black spots on shower grout, caulk, tile, and curtains are usually surface mold or mildew feeding on soap residue and daily moisture, not Stachybotrys. They are still worth cleaning:
- Scrub with detergent and water and dry the surface
- Replace caulk that stays stained, since growth can get into it
- Run the exhaust fan during and after showers
If dark growth appears on the painted ceiling or wall outside the shower, or the drywall behind the tile feels soft, there may be a leak inside the wall. See mold vs. mildew.
Things that look like mold but are not
| Look-alike | How it differs from mold |
|---|---|
| Soot from candles, a fireplace, or a furnace | Gray-black smudges, often on ceilings above candles or near vents; dry and powdery; no musty smell |
| Dust lines along framing ("ghosting") | Straight lines or stripes that follow studs, joists, or ceiling framing on exterior walls |
| Dirt and grime | Found where hands or furniture touch; wipes off without staining |
| Water stains | Brown or yellow rings with defined edges; a sign of a leak, and a reason to check for mold nearby |
| Rust | Orange-brown, near metal fasteners, pipes, or fixtures |
A useful rule: mold almost always comes with moisture. If the surface is dry, has never been wet, and has no musty smell, the stain may be something else. If there is staining, softness, or a smell, treat it as mold until shown otherwise.
Where to look
If you have seen one patch, check the places where water collects or travels:
- Under sinks and around toilets, tubs, and showers
- Ceilings below bathrooms and under the roof
- Around windows and exterior doors
- The air conditioning closet, drain pan, and vents
- Behind the refrigerator and washing machine
- Basements, crawl spaces, and the lower part of walls after any flooding
The EPA notes that mold can grow on hidden surfaces too, including the back side of drywall, wallpaper, paneling, the top of ceiling tiles, and the underside of carpets and pads. Our guide on signs of mold in your house covers what to watch for.
Can you confirm it is black mold?
Only a lab can identify the species, from a tape, swab, or material sample. For most homes, that step is optional. The EPA says that in most cases, if mold growth is visible, sampling is unnecessary, and the CDC says it is not necessary to determine what type of mold you have, because all molds should be treated the same way. Testing is most useful when you suspect hidden growth, need documentation for an insurance claim or a sale, or want to confirm that cleanup worked. See what a mold inspection involves.
If you think you found black mold
- Do not disturb a large area. Scrubbing, scraping, or tearing out moldy material without protection can spread spores.
- Find the moisture. Look for the leak, drain, or condensation feeding it, and stop it.
- Estimate the size. Under about 10 square feet on a hard surface can often be a careful DIY job. Remember that growth on the back of drywall is often larger than the stain on the front.
- Photograph it. Dated photos help with insurance claims, landlord notices, and quotes.
- Get help for larger or hidden growth. Mold on drywall, insulation, or in the air conditioning system usually needs a professional. See DIY vs. professional mold removal.
If anyone in the home has asthma, a mold allergy, or a weakened immune system, keep them away from the area and talk to a doctor about any symptoms. Our guide is black mold dangerous? summarizes what health agencies say.
Next step
If you own your home and the dark growth is larger than a small patch, sits on drywall, or keeps coming back, call the number on this page to be connected with an independent local mold inspection or mold removal company.