Stachybotrys is a greenish black mold that grows on material with a high cellulose content or such as hay, straw, wicker, and wood chips, as well as building materials such as ceiling tile, drywall, paper vapor barriers, wallpaper, insulation backing, cardboard boxes, paper files, fiberboard, the paper covering of gypsum wallboard, particleboard, jute, dust, and wood when these items become water damaged. This mold requires very wet or high humid conditions for days or weeks in order to grow. Excessive indoor humidity resulting in water vapor condensation on walls, plumbing leaks, spills from showering or bathing, water leaking through foundations or roofs may lead to growth of many types of mold, including stachybotrys.

Individuals with chronic exposure to toxins produced by this fungus reported cold and flu symptoms, memory loss, muscle aches, sore throats, diarrhea, headaches, fatigue, dermatitis, intermittent local hair loss, cancer, and generalized malaise. The toxins produced by this fungus will suppress and could destroy the immune system affecting the lymphoid tissue and the bone marrow. Animals injected with the toxin from this fungus exhibited the following symptoms: necrosis and hemorrhage within the brain, thymus, spleen, intestine, lung, heart, lymph node, liver, and kidney. Affects by absorption of the toxin in the human lung are known as pneumomycosis. The toxins may also suppress the immune system. In the January 17 issue of the MMWR, stachybotrys was implicated in a cluster of fatal pulmonary hemorrhage/hemosiderosis among infants.

In the past several years, case-control studies of occupational exposure to stachybotrys in water-damaged building environments have generated much controversy. In one of these investigations, significant differences in self-reported symptoms (chronic fatigue, dermatologic, constitutional, and lower respiratory tract) between cases (n=51) and controls (n=21) were attributed to exposure to stachybotrys and other "atypical fungi." The study design did not include an evaluation for water damage or the presence of these fungi in the work or living environments of control subjects.

Speculation that exposure to stachybotrys produced immune dysfunction in cases was based on observations that cases had a lower proportion of mature T-lymphocyte (CD3) cells than controls (74% vs 76%, respectively), a finding that was statistically significant. The clinical significance of this finding remains difficult to interpret, and could have been affected by laboratory as well as individual daily variation. More important, this observation was the only one of over 20 hematologic and immunologic comparisons made between cases and controls that was found to be statistically significant, an observation that could be explained by chance.

In another case-control study, which concluded that exposure to stachybotrys and other toxigenic fungi was responsible for various pulmonary diseases (including asthma, interstitial lung disease, and "emphysematous-like" disease) among office workers in a water-damaged building, no reliable biomarkers of exposure to stachybotrys or radiographic findings correlating with the self-reported pulmonary symptoms were present.