"Black mold" is a common name, not a scientific one. It almost always refers to Stachybotrys chartarum — but dozens of unrelated species also grow black, and the one thing they have in common is that you cannot tell them apart by looking.
Stachybotrys chartarum is a microfungus first described scientifically in 1818, by Christian Gottfried Ehrenberg, who noted that it adheres to paper and sometimes forms circles dotted with black. It was moved into the genus Stachybotrys in 1958.
It is a slow grower that does not compete well against other molds, and it is only rarely found in nature. Indoors it is a different story: it is most often detected in cellulose-rich building materials such as gypsum drywall and wallpaper in damp or water-damaged buildings. It favours conditions with large amounts of cellulose, low nitrogen, no sunlight, no competing molds, and constant humidity — which describes the inside of a wall cavity after a leak almost exactly.
There are two chemotypes of the species. One produces trichothecene mycotoxins, including satratoxin H; the other produces compounds called atranones. Not every strain produces mycotoxins at all, and high indoor humidity on its own does not mean a mycotoxin-producing strain is present. Spores are released into the air when the colony is mechanically disturbed — particularly while it is wet, which is exactly what scrubbing at it accomplishes.
| Kingdom | Fungi |
| Division | Ascomycota |
| Class | Sordariomycetes |
| Order | Hypocreales |
| Family | Stachybotryaceae |
| Species | S. chartarum |
A leak, a flood, condensation or humidity that never fully dries. Growth can begin within 24 to 48 hours of water intrusion.
Drywall paper, wallpaper, ceiling tiles, cardboard, wood, natural-fibre carpet. Ordinary house construction is a food supply.
No sunlight, little air movement, no competing molds. Wall cavities, crawlspaces and closed-off basements qualify.
Because it grows slowly and competes poorly, a Stachybotrys colony usually means the damp has been there a long while.
The adverse health effects of mold contamination are widely known. Fatigue, weakness, headaches, joint stiffness, shortness of breath, sinus congestion and chronic cough are a few of the ailments associated with mold exposure. The very young, the old, pets and people with compromised immune systems are particularly at risk.
Claims of health problems in humans and animals linked to this mold have been made since the 1930s, and more recently it has been associated with so-called sick building syndrome. That particular link has not been firmly established in the scientific literature, and a widely reported 1994 investigation connecting the mold to infant pulmonary haemorrhage in Cleveland was later found by the CDC to have analysed its data incorrectly.
What is not in dispute: mold spores are a recognised respiratory irritant and allergen, several indoor species produce mycotoxins, and the standard public-health advice is to remove the moisture and the growth rather than to live with them. Testing tells you which species you have and how much of it is in your air, so the decision is based on measurement instead of on argument.
A black patch on a wall could be Stachybotrys. It could equally be Cladosporium, the most commonly identified airborne mold in the world; Aspergillus niger, whose black spore heads are a fixture of damp bathrooms; Alternaria, which is dark brown to black and heavily allergenic; or Aureobasidium, which turns bathroom caulk black as it matures. Colour, texture and location narrow the field. They do not settle it.
Spores are released when the colony is disturbed, especially while wet. Scrubbing a patch is the most efficient way to move it into the air you breathe.
Shut the door, stop using the space if you reasonably can, and do not run fans or the HVAC system into the rest of the house.
Date-stamped photographs of the growth and of the water source matter later, to an insurer, a landlord or a buyer.
Sampling identifies the species and measures the spore count against an outdoor baseline, in writing, from an independent laboratory.
We test and document only, so the report has nothing to sell you. Same-day appointments in Suffolk County, lab results usually within 48 hours.
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