Is This Black Mold? Six Myths, and What the Dark Spots Usually Are

By John Calhoun, owner of Mold Remediation Gettysburg PA · Updated October 26, 2026

“Is this black mold?” is one of the most common questions in this business, usually asked about a dark patch behind a dresser or on a basement wall. It’s a fair question with a surprising answer: black mold isn’t a species. The EPA’s mold course says it in one line, that neither black mold nor toxic mold is a specific kind of mold, and that no one can tell whether a mold is producing toxins just by looking at it. Dark color is common. What matters is what it’s growing on and why that material stayed wet.

So don’t stress. It can be fixed. Here are the myths I hear most, and what the evidence says.

Myth 1: Black mold is one particular mold

The mold most people mean is Stachybotrys chartarum, which the CDC describes as greenish-black. But plenty of other common indoor molds are dark too. Cladosporium, for instance, grows olive-green to olive-brown on top and greenish-black underneath in the lab, and Quebec’s public health institute reports it was found in about 70% of U.S. homes examined in one survey. On a wet window frame it can form a velvety olive-green layer that most people would call black mold without a second thought.

Myth 2: Black means it’s the dangerous one

Color tells you about pigment, not species or risk. The CDC’s own description is that mold shows up in all sorts of colors, and the EPA’s point stands: you can’t judge what a mold is producing by looking at it. I’m not going to make health claims either way. For that, read the CDC’s mold pages. For what color can and can’t tell you, see white, green, orange and pink growth.

Myth 3: Stachybotrys pops up after any little leak

It’s actually picky and slow. Quebec’s public health institute says it needs a lot of water (a water activity of at least 0.94, best above 0.98), favors material that’s high in cellulose and low in nitrogen, and grows slowly enough that faster molds tend to crowd it out. It starts out white and turns blackish-green as it ages. Its favorite places are drywall paper, ceiling tile and paper vapor barriers that have been wet for a long time.

That makes it a useful clue. Finding it usually means a material has stayed wet for weeks, not hours.

Myth 4: Every dark spot is the same mold

You can’t identify a species by its color, but a 2011 field study of water-damaged buildings, published in Applied and Environmental Microbiology, found clear patterns between molds and the materials they grew on:

So the dark patch on basement concrete is a different likely cast of characters than the dark patch on the back of a bathroom wall.

Myth 5: You need a test to know what to do

The CDC doesn’t recommend mold testing for most homes and says you don’t need to know the type of mold, because whatever is there needs to be removed. And there’s no federal yardstick: the EPA’s testing page notes no federal limits have been set for mold or spores, so a lab number has nothing official to be measured against. If you can already see the growth, the EPA treats sampling as usually not needed. There are good reasons to sample, covered in mold inspection vs. mold testing, but “is it black mold?” usually isn’t one of them.

Myth 6: Black mold needs a special, pricier removal

The CDC says all molds should be treated the same with respect to removal. The method is set by the material and the size of the area: clean hard surfaces, remove porous material that’s grown through, contain bigger jobs, and fix the water. More on that in mold behind drywall.

Where the scare came from

Much of the fear traces back to a CDC investigation of a cluster of infant illnesses in Cleveland in the mid-1990s, which reported an association with Stachybotrys in water-damaged homes. In March 2000, CDC reviewers published a reanalysis in the Morbidity and Mortality Weekly Report concluding the associations should be considered not proven. Among the problems they found: one investigator had collected twice as many air samples from the homes of sick children as from the comparison homes. I mention it because the scare stuck around long after the review did.

What a flood or a slow leak leaves behind

A long-wet material is exactly what a flood or a slow leak leaves behind. FEMA’s flood insurance records list 83 claims in the Gettysburg ZIP code, 17325, since 1978, and in the borough about 87% of homes were built before 1980, per Census estimates. The Gettysburg housing data page has both. When I find growth that looks like Stachybotrys, the next thing I want is the moisture history of that wall.

This is John Calhoun at Mold Remediation Gettysburg PA. Whatever color it is, I’ll find out why it stayed wet and show you the readings. How I handle the cleanup is on the mold remediation in Gettysburg, PA page, and the list of mold services breaks it down.