A mold injury claim turns on one question: did the mold in this home make this person sick? For years, landlords answered by arguing that mold is everywhere and that no test could tie a family's illness to one building. Modern laboratory science has changed that answer. Testing can now identify specific mold species in the home and an immune response to those same species in the person.
Physicians and lawyers call this connection a biological match. It does not rest on a hunch or a list of symptoms alone. It rests on DNA testing of the home, blood and urine testing of the person, and a physician's examination tying the two together. This article explains how each piece works, where the science enjoys acceptance, and where its limits lie.
The key tool is polymerase chain reaction (PCR). PCR copies a tiny fragment of genetic material millions of times until a laboratory can detect and count it. Its inventor, Kary Mullis, shared the 1993 Nobel Prize in Chemistry for the discovery. Crime laboratories rely on PCR to match DNA from a crime scene to a suspect, and courts across the country admit that evidence every day.
Most Americans met PCR during the pandemic. The standard COVID-19 swab test used a form of PCR to find the virus's genetic code in a nasal sample. The same principle applies to mold. Each mold species carries its own DNA signature, so a laboratory can identify Stachybotrys chartarum or Aspergillus versicolor by name and count how much of it a sample holds.
Scientists at the United States Environmental Protection Agency (EPA) developed mold specific quantitative PCR to measure 36 mold species in settled household dust. The Department of Housing and Urban Development (HUD) then used the method in its 2006 American Healthy Homes Survey of roughly 1,100 homes nationwide. That work sorted the 36 species into 26 linked to water damage and 10 found in most homes regardless of water.
Settled dust matters because it records months or years of accumulation, not a single afternoon. A swab from a stained wall or an air return can be tested the same way. Certain molds, such as Stachybotrys and Chaetomium, grow only on materials that stayed wet for long periods. Finding them by DNA therefore proves a sustained water problem, even after a landlord has painted over the damage.
One caution deserves mention. The EPA built its Environmental Relative Moldiness Index (ERMI), a single score drawn from those 36 species, as a research tool, and its Inspector General has warned that the public uses it for decisions it was not designed to make. The species counts themselves, reported by an accredited laboratory, carry the real value. You can read more in our article on what a thorough mold inspection looks like.
Testing strengthens a case, but its absence does not end one. Landlords sometimes repair or remove the damage before anyone takes a sample, and some families cannot afford testing. In those cases, an expert such as a certified mold assessor or industrial hygienist can examine photographs, videos, repair records and the home itself, and testify that the growth they show is mold.
Assessors at the Safe Housing Collaborative conference described assessment as ninety percent of the job and sampling as only ten percent. A thorough assessor often finds the mold without needing samples. Tide lines, swollen baseboards, cupped flooring, fresh paint over stains and musty odors all record past water, and maintenance work orders and tenant complaints document both the water and the landlord's notice.
Other witnesses can establish the mold as well. A county or city housing inspector who cites a property for mold creates an official record of what the inspector saw. A landlord's own maintenance workers, property managers and contractors often acknowledge the mold in work orders, e-mails or testimony. Under Maryland Rule 5-803(a), statements by a party's employees about matters within their jobs can come into evidence against that party.
The leading health research rests largely on the same kind of evidence. The Institute of Medicine and the World Health Organization drew their conclusions from studies of visible dampness, visible mold and musty odors in homes, not from laboratory samples alone. Photographs and an expert's trained eye therefore speak the same language as the science. Testing, where available, adds precision to that picture rather than replacing it.
On the medical side, treating physicians and allergists choose from several tests. Each answers a different question, and none stands alone. The choice of tests always belongs to the physician, who weighs the patient's history and symptoms.
Specific IgE testing is a standard allergy test. It measures whether the immune system has become sensitized to particular molds, such as Aspergillus fumigatus or Cladosporium herbarum. Allergists caution that sensitization alone does not prove allergic disease. When a positive result lines up with symptoms that began in the home and eased after leaving it, however, the test carries real weight.
Specific IgG testing shows that a person's immune system has met a particular mold and mounted a response to it. Allergists treat an elevated IgG as evidence of exposure rather than as a diagnosis. That limit makes IgG especially useful for the match. An elevated IgG to Penicillium or Stachybotrys, the same species PCR found in the home, ties the person to that building.
Laboratories such as RealTime Laboratories and Mosaic Diagnostics test urine for mycotoxins, the toxic compounds some molds produce. A result showing citrinin, for example, points to Aspergillus or Penicillium, both known producers of that toxin. Medical toxicology and allergy organizations have criticized some of these tests, so their value depends on a physician who interprets them alongside the home testing and the medical history.
Some physicians order human leukocyte antigen (HLA-DR/DQ) testing to look for gene variants that published case reports associate with lingering mold-related illness. This research remains young, and the defense often challenges it. It may still help a physician explain why one family member recovered after moving out while another did not.
Physicians also rely on familiar tests, including allergy skin testing, breathing tests (pulmonary function tests), and chest imaging. These document the injury itself.
The match puts the pieces side by side. PCR finds Aspergillus versicolor and Penicillium in the dust of a family's apartment. Blood testing then shows elevated antibodies to Aspergillus and Penicillium in the people who lived there. Professor Vanessa L. Johnson of the University of Houston-Clear Lake explains that modern laboratory methods can now match what a contaminated home holds with what an exposed person carries, which supplies case-specific proof of exposure (Toxic Mold Litigation: Causation Should No Longer Be Controversial, 56 Cumb. L. Rev. 221 (2026)).
Maryland courts decide whether expert testimony reaches a jury under Maryland Rule 5-702. In Rochkind v. Stevenson, 471 Md. 1 (2020), the Supreme Court of Maryland adopted the federal Daubert approach. Judges now ask whether a method has been tested, published and peer reviewed, whether it has a known error rate, and whether the scientific community accepts it. PCR answers each question well, because forensic, medical and public health laboratories use it daily.
The courts have also shown what fails. In Chesson v. Montgomery Mutual Insurance Co., 434 Md. 346 (2013), Maryland's highest court held that a mold diagnosis resting on a contested methodology should not have reached the jury. The lesson favors the biological match. Proof resting on accepted laboratory methods, applied to this home and this person, stands on far firmer ground than a theory of illness alone.
The physician then completes the picture through a differential diagnosis. At the Safe Housing Collaborative conference in Austin in October 2026, a physician speaker described the method plainly. The treating doctor examines the patient, rules in mold exposure, and rules out other causes, with the home's mold reports in hand. The resulting opinion must state whether mold was, more likely than not, a substantial factor in the illness.
Evidence of mold disappears quickly once a landlord starts repairs, so the first step is to capture it. Ask an industrial hygienist or mold inspector about settled dust and swab samples analyzed by PCR at an accredited laboratory, along with air samples. Photograph every stain, leak and patch of growth, and keep every repair request and reply. If the damage is already gone, those photographs and records still give an expert something to work with.
Your health comes first. If new symptoms begin after exposure to mold or water-damaged building materials, including exposure you did not recognize at the time, see your physician for care. Tell the physician where you live and what any testing found, because that history helps the doctor diagnose and treat you. Your physician decides which tests fit your history, and you should keep copies of every result.
To discuss a Maryland mold injury claim, e-mail chris@attorneybeard.com or call (410) 267-0227.
