Understanding Mold and Mold Lawsuits

William L. Porter Founder & President Specializing in Construction Law, Business Law and Labor Law
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Recent years have seen an explosion of mold litigation with the publication of several multimillion dollar jury verdicts in toxic mold lawsuits. While large plaintiff’s verdicts are well publicized, defense verdicts in mold cases rarely, if ever, receive public notice. Prior to 2000, relatively few mold claims were pursued, and claims were routinely settled for nominal amounts – $5,000 or less. Since then highly publicized seven and even eight figure jury verdicts have led to a proliferation of mold litigation. U.S. insurers paid $1.3 billion in mold-related claims in 2001 and more than $3 billion in 2002¹ Medical opinion on mold related disease is evolving, and many mold injury cases are pursued without solid medical or scientific support.

Commonly, a mold claim seeks to bring personal injury and property damage claims into a lawsuit seeking recovery for: 1) Construction defects; 2) Landlord/tenant breach of warranty of habitability; and 3) Failure to disclose defects in a real estate sale. Mold claims may also arise in worker’s compensation and insurance bad faith disputes. Understanding the current status of medical and scientific opinion on mold is important to effectively pursue or defend a mold injury claim.

Mold has been around since the dawn of life. Mold is a form of fungus. Although a plant-like organism, it differs from plants in that it doesn’t use photosynthesis (sunlight) to survive and propagate. Molds feed on organic material, decomposing it in the process. Mold spores are microscopic “seeds” that enable mold to propagate and spread. Mold spores are present in the air everywhere, both indoors and outdoors.

Not all mold is harmful. Certain mold species turn milk into cheese and soybeans into soy sauce. Mold is used to create citric acid, a commonly used food preservative. Penicillin is an antibiotic derived from bread mold.

There is general agreement that many types of mold are harmful to human beings. The medical community accepts that inhalation of mold spores and mold particles can trigger allergic reactions in sensitized individuals. Persons with compromised immune systems are more susceptible to mold infection than the general population. There is, however, significant disagreement in the medical community as to the degree that exposure to elevated levels of air borne toxic mold can cause disease in the average person.

Certain types of environmental molds, such as Aspergillus, Penicillium, Cladosporium and Stachybotrys, develop and grow on organic building materials, such as wood and gypsum drywall, when those materials become wet. When large quantities of these molds are inhaled over long periods of time, live mold spores can lodge in the sinus and lung tissues and can colonize. This triggers an immunological reaction, causing flu like symptoms that can include congestion, pneumonia, headaches, achy joints and fatigue. Many of the symptoms of a mold infection are the result of the body’s mobilization of its immune system to fight mold exposure. Some medical studies have concluded that long term exposure to toxic molds can lead to “hyper immune” reactions causing chemical and other environmental hyper-sensitivities.

Certain molds also produce toxic chemicals known as “mycotoxins”. There is considerable controversy as to whether air borne mold exposure can result in exposure to sufficient levels of such mycotoxins to actually constitute a significant health hazard.

There is general agreement that long term exposure to extremely high levels of environmental molds such as Penicillium and Aspergillus can cause health problems. However, there are no currently established scientific guidelines for determining the exact levels of mold exposure which constitute a hazard. The diagnostic criteria for determining mold related health conditions is evolving as well. The diagnostic methods of several so-called “mold doctors” have been successfully challenged and discredited in court.

There is emerging medical evidence that mold infections can be diagnosed through blood testing that looks for elevated levels of antibodies to specific molds. Mold exposure via infection triggers an immunological reaction, similar in effect to a viral infection. The body’s immune system reacts by creating antibodies that attack and neutralize the specific mold. In theory, a doctor can diagnose a mold related health condition by identifying the presence of mold-specific antibodies in a person’s blood serum. Laboratory testing methods for mold antibodies has not yet been generally accepted in the medical community and can be legally challenged under Kelly/Frye standards.

Medical treatment of mold related health conditions is similarly controversial. Certain antifungal medications, combined with dietary and environmental changes have shown positive results in treating mold related health conditions. Fortunately, there is little evidence that mold exposure can lead to a serious long term health impact, particularly where the patient receives proper medical attention early on.

Mold grows when certain organic building materials are exposed to water, particularly in dark, warm environments. Mold is commonly found on drywall and wood that has been exposed to significant moisture over time. Leaky windows, stucco, roofs and plumbing are the most common culprits. When water enters interior walls an ideal environment for mold growth can exist. Over time, the mold can grow through the drywall and become visible as discoloration on interior walls. In addition, poor exterior drainage can cause water saturation of a slab foundation, which can lead to mold growth on interior flooring and walls.

Upon learning of a mold related claim, it is extremely important to hire a qualified industrial hygienist to investigate and test the affected premises. Accurate testing and evaluation is key to determining whether elevated mold levels are present in a living area. Air sampling for viable and non-viable mold spores is a common practice used to detect the elevated levels of air borne mold spores. Interior air samples are compared to samples taken outside the dwelling to determine whether elevated levels of mold are present inside the dwelling. The levels of elevated mold readings inside a dwelling can be one clue in determining whether a health impact may exist.

If it appears that mold levels inside the dwelling are significantly elevated, the next step is to identify the cause and source of water intrusion in the work or living space. Water intrusion testing with cameras using infrared film is a common method of identifying and locating the cause and source of water intrusion. Destructive testing is typically performed to determine the precise structural conditions that allow water intrusion into the dwelling. Slab foundation moisture testing is a standard means of determining if the foundation is adversely affected by water.

Mold remediation involves removing the affected materials and repairing the source of the water intrusion. This is generally done under carefully controlled conditions. The mold contaminated area is sealed off from the remaining portion of the unit and the contaminated material is removed under negative air pressure to prevent the spread of airborne mold spores. A qualified mold remediation contractor should be used for this process. Personal property that has been contaminated by mold should also be cleaned or discarded.

Proper and prompt steps to investigate and remediate mold should be taken if a property owner suspects the presence of mold. Ignoring the problem, or dealing with it ineffectively, can lead to significantly increased potential liability down the road.

If it is determined that a person has been exposed to elevated levels of hazardous environmental molds from an identified cause and source, the next step is to determine whether the exposure has led to a legitimate health impact. An analysis of the claim includes a detailed review of the claimant’s medical history. Are a person’s symptoms consistent with a mold related health condition? How long has the person exhibited such symptoms? Is the level of mold exposure sufficient to create a colorable health claim? As with any personal injury claim, pre-existing medical conditions should also be considered.

From a plaintiff’s perspective, it is important to obtain a diagnosis of a mold related condition from a qualified medical professional. The foundation of a mold diagnosis and the diagnostic criteria must be sound. This can be difficult, as the general medical community has been slow to accept mold related health conditions as a standard, accepted diagnosis.

From a defense standpoint, it is important to consider the validity of a mold diagnosis on multiple levels. The scientific and medical validity of the doctor’s testing and diagnostic criteria should be carefully reviewed. Retaining a qualified medical professional to review and, where appropriate, challenge the treating physician’s testing, diagnosis and prognosis is a critical key to successfully defending a mold personal injury claim.

If the plaintiff’s treating physician is a professional “mold doctor”, his or her credibility may be a major issue in defending a mold claim. Certain doctors have become “specialists” in the diagnosis and treatment of mold related health conditions. Such doctors can also become professional expert witnesses, making a significant living by testifying in mold injury cases. The credibility of such medical professionals may be suspect, as they often have a financial incentive to over-diagnose or exaggerate the severity of mold related health conditions. Prior testimony in other lawsuits may be useful in attacking a mold doctor’s credibility.

A common, and often highly effective defense strategy, is to seek to exclude from evidence, by way of pretrial motions in limine, the plaintiff’s doctor’s testing and other diagnostic methodologies as scientifically unreliable.


As noted above, personal injury damages in mold cases have ranged from millions of dollars to zero. Seven figure jury verdicts appear to have become less common as the defense bar has become more adept at understanding the issues and developing effective strategies for defending mold claims.


The health effects of mold have generated considerable controversy. A fair amount of hysteria now exists in the public and among industry groups. The proliferation of mold lawsuits has been in large part driven by plaintiffs, attorneys and doctors. A financial motive is often viewed as the driving force for many of these claims. Some of the murky issues regarding mold will receive greater clarity in the future as medical and scientific research progresses. It is likely that standard guidance on the diagnosis and treatment of mold related health conditions will emerge. Hopefully, in the future, the mold issues currently at hand will be viewed as commonplace as any other environmental allergen and treated as such.

¹Insurance Information Institute. “Mold and Insurance” by Robert P. Hartwig and Claire Wilkonson at 3 Insurance Issues Series, Vol. 1, Number 4 (2003)

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