The Ultimate Guide to Mold

As you may have noticed, media reports often suggest that mold is a pervasive and dangerous organism present in the environments where we live, learn, and work. In this Ultimate Guide to Mold we’re going to dig in to how accurate this perception really is and how to optimize your indoor air quality.

• Is mold truly infiltrating our homes so that it significantly contaminates indoor air with harmful substances?
• Are certain molds and fungi genuinely life-threatening to us?
• What health risks are typically associated with mold exposure?
• How can we effectively prevent mold issues in buildings, and what actions should be taken if active mold is found or suspected?

These are some of the key questions we aim to address here. Terms like mold, rot, and mildew are commonly used interchangeably to describe various fungal growths.

Specialists in mycology often refer to fuzzy or woolly fungal colonies on surfaces such as wood, paper, or spoiled foods as mold, while mildew specifically denotes fungal growth on fabrics. In this guide, we will use the terms fungi and mold interchangeably.

Many news articles tend to highlight the adverse effects of black mold, and it is accurate that mold exposure can pose challenges for humans. It can lead to the early decay of wooden structures, and exposure to high levels of any mold type may result in health issues.

However, it’s also important to recognize that mold also offers numerous advantages. For instance, many people enjoy consuming mushrooms, which are the fruiting bodies of certain molds. Yeast, used in bread-making and brewing, is another form of mold.

In our ecosystem, mold plays a crucial role by decomposing dead plant matter, therefore recycling nutrients back into the soil to support new growth. Without mold’s decomposition capabilities, our world would quickly become overwhelmed with accumulated dead foliage and plant material.

Fungal Organisms – Background Information

Research indicates that fungal organisms make up about 25% of the earth’s biomass, highlighting their extensive presence in our environment.

Fungi primarily feed on the remains of dead plants and animals. Remarkably, they are among the few organisms capable of decomposing wood and wood-based materials like cardboard and paper into simpler, digestible compounds.

Considering that most homes are built with wood and contain wooden furniture, cabinets, and items such as books and newspapers, our living spaces provide abundant food sources for these fungi and sometimes require mold remediation. Remediation practices eliminate the sources of mold growth, remove contaminated materials, install measures to control humidity levels and create conditions where the indoor environment is both beneficial to the structural integrity of the building and the health of the inhabitants.

In addition to a nutrient source, mold thrives in environments where temperatures range from 40°F to 100°F and where there is a considerable amount of moisture.

As previously mentioned, homes offer an abundance of food sources for fungi, and the typical household temperature range is highly favorable for mold expansion.

The moisture content within these nutrient sources plays a pivotal role in determining whether fungi can germinate and develop on a surface. Fungi have a preference for food materials that are quite damp, with saturation levels of 70% to 80% or higher.

In residential buildings, condensation serves as the primary source of moisture that saturates these food sources, facilitating mold and reduced air quality.

Fungi, similar to other living organisms, produce by-products while decomposing food sources into essential nutrients. During the conversion of carbohydrates into energy, various fungal species emit certain substances as by-products of their physical and chemical transformations. These substances include:

• Carbon Dioxide (CO₂)
• Water (H₂0)
• Volatile Organic Compounds (mVOC)
• Mycotoxins (Tm)

The musty odor often linked to mold is a result of the VOCs emitted by molds. It is important to note that the potential health effects of these fungal VOCs have not been thoroughly researched.

Mycotoxins

In addition to the previously mentioned by-products, certain mold species also emit secondary compounds known as mycotoxins.

Mold spores generate these mycotoxins to safeguard their nutritional resources from competing organisms such as bacteria and other fungal species.

A well-known example of a mycotoxin is penicillin, produced by some species within the PenicilliumPenicilliumPenicillium is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production like penicillin, a molecule that is used as an antibiotic, which kills or stops the growth of certain kinds of bacteria. genus. Penicillin exhibits high toxicity towards bacteria, a property that humans have harnessed to combat bacterial infections.

However, it’s important to note that some fungal mycotoxins are also harmful to mammals, including humans. For instance, Aflatoxin is a mycotoxin produced by molds that often thrive on spoiled foods, particularly feed grains and peanuts. It is an exceptionally potent carcinogen, surpassing many industrial chemical compounds in its cancer-causing potential.

Another example is Tricothecene (T-2), a mycotoxin produced by molds that poses a risk to human health.

Fungi are prolific producers of mold spores, which serve a similar purpose to seeds in plants. These mold spores are the reproductive units of fungi. Once released into the air, they can settle in environments with suitable conditions – such as moisture and a nutrient source – and germinate, leading to new fungal growth.

Fungi and Health Problems

Exposure to fungi create health problems for humans in three basic ways:

• Allergic Reactions
• Fungal Infections
• Mycotoxicosis

Allergic Reactions

An allergy develops when an individual is exposed to a substance, leading to sensitization. During this phase, the body’s immune system generates antibodies specifically targeting the allergen – the substance causing sensitization.

Once sensitization is complete, further exposure to the allergen can trigger physical symptoms such as sneezing and coughing. These symptoms are not due to the allergen attacking the body directly; rather, they result from chemicals released by the immune system in response to the allergen’s presence.

Essentially, an allergy is characterized by the immune system’s excessive response to substances that generally do not affect most people, as defined by the Asthma and Allergy Foundation of America.

It is widely recognized that contact with fungi may provoke respiratory allergies; however, research suggests that only a small proportion of individuals are susceptible to allergic reactions from mold exposure.

Listed below are allergy related problems caused by mold exposure.

Rhinitis:

This allergic reaction closely resembles the symptoms typically associated with the common cold, such as nasal congestion, a runny nose, sneezing, itching of the nose and eyes, and watery eyes.

Although these symptoms can be uncomfortable, they are rarely life-threatening. However, if the person experiencing the allergic reaction also suffers from asthma, exposure to allergens can trigger or worsen an asthma attack. Asthma attacks can pose significant risks to health and may become life-threatening emergencies.

Hypersensitivity Pneumonitis:

This is an allergic reaction triggered by inhaling organic or chemical allergens. When fungi are the culprits, this condition often arises from breathing in a significant concentration of mold spores from moldy agricultural materials, such as hay or silage.

Commonly referred to as “farmer’s lung“, the acute form of this illness typically follows substantial exposure to these antigens.

Individuals may experience symptoms such as fever, chills, and difficulty breathing, which generally subside 4 to 12 hours after exposure. However, these symptoms are likely to reappear upon subsequent exposure. If measures are not taken to prevent future contact with the allergen, there is a risk of developing chronic lung disease.

Fungal Infections (Mycosis)

Fungal infections occur when fungi exploit human body tissues as a source of nourishment. Common examples include Athlete’s Foot and Ringworm, which affect the skin.

Beyond the skin, certain fungal infections can infiltrate the respiratory system and other internal organs. Aspergillosis is one such infection, arising from inhaling spores of four Aspergillus species. These mold spores are prevalent in various environments, including homes, offices, and hospitals.

Aspergillosis primarily affects individuals with severely compromised immune systems or chronic lung conditions, such as COPD, AIDS patients, or those undergoing cancer treatments. For most individuals with healthy immune systems, fungal infections of the respiratory tract are effectively warded off.

Mycotoxicosis

As previously mentioned, numerous fungi species produce mycotoxins as a defense mechanism to safeguard their food supply from other organisms. This can be likened to a form of biological warfare employed by these fungal organisms. Unfortunately, these mycotoxins pose a risk to human health.

The term “mycotoxicosis” describes illnesses that arise from exposure to these toxic substances. Although Stachybotrys chartarumStachybotrys chartarumStachybotrys chartarum also known as black mold is a species of microfungus that produces its conidia in slime heads. Because of misinformation, S. chartarum has been inappropriately referred to as toxic mold. A variety of health problems have been misattributed to S. chartarum. is frequently highlighted in media reports as the infamous “toxic black mold,” several species of CladosporiumCladosporiumCladosporium which can grow both indoors and outdoors is a common mold that may affect your health. While most species of Cladosporium aren’t dangerous to humans, they can cause allergies and asthma in some people. In very rare cases, it can be potentially dangerous, causing a fungal infection in the lungs., PenicilliumPenicilliumPenicillium is a genus of ascomycetous fungi that is part of the mycobiome of many species and is of major importance in the natural environment, in food spoilage, and in food and drug production like penicillin, a molecule that is used as an antibiotic, which kills or stops the growth of certain kinds of bacteria., FusariumFusariumMost Fusarium species are soil fungi and some are plant pathogens, causing root and stem rot, vascular wilt or fruit rot and are important mycotoxin producers. Several species have emerged as important opportunistic pathogens in humans causing hyalohyphomycosis, mycotic keratitis and onychomycosis., and AspergillusAspergillusAspergillum is an asexual spore-forming structure common to all Aspergillus species; around one-third of species are also known to have a sexual stage. While some species of Aspergillus are known to cause fungal infections, others are of commercial importance. are also capable of producing mycotoxins.

These four are among the most prevalent airborne fungi found both indoors and outdoors, making it essential to avoid any significant and/or prolonged exposure.

How significant is the threat of fungal mycotoxins to human health?

It is well-documented that consuming food contaminated with mycotoxins can lead to illness. Historical accounts reveal several fatal epidemics in Russia during the 1940s, attributed to the consumption of wheat tainted with tricothecene, a mycotoxin produced by various common fungi species. Similarly, a series of mold-related poisonings occurred in India in 1987.

Among these fungi, the Aspergillus species – specifically Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger, and Aspergillus terreus – are of particular concern.

Although not the only pathogen in this genus, (more than 900 species are included in the genus Aspergillus), it is estimated that Aspergillus fumigatus is considered the most common etiologic agent for human infections, responsible for approximately 90% of the cases related to Aspergillus infection.

Investigations revealed that the cases of poisoning were linked to the consumption of bread made from wheat contaminated with Aspergillus and Fusarium fungi, both of which are known to produce trichothecene-based mycotoxins. Tests on the wheat confirmed the presence of various trichothecene toxins.

Once individuals ceased using this contaminated wheat for bread-making, the illnesses subsided. It is also established that inhaling mycotoxins can pose health risks to humans.

A documented incident of mycotoxin-related illness due to inhalation occurred in Russia during the 1940s, affecting farm workers who handled and transported moldy hay.

These workers experienced symptoms such as respiratory difficulties, sore throats, nosebleeds, and severe skin rashes. Cultures from skin samples of affected individuals and samples from the hay revealed Stachybotrys chartarum, establishing a link between exposure to the moldy hay and the workers’ illnesses. This condition, known as stachybotryotoxicosis, resolved within a week after discontinuing exposure to the moldy hay.

According to the United States Centers for Disease Control (CDC), stachybotryotoxicosis is not uncommon in industrial environments like cotton-seed oil mills, grain elevators, and malt grain processing facilities. However, there is no definitive scientific evidence indicating that mycotoxins produced by Stachybotrys chartarum or other toxic molds reach harmful concentrations in residential or commercial settings such as homes, offices, or schools.

Nevertheless, it is prudent to prioritize safety and recognize that exposure to active mold and its spores can be detrimental to health. Therefore, it is essential to manage and control mold growth in any environment where people live or work.

Controlling Mold Growth

The ubiquitous presence of mold spores in both indoor and outdoor environments can make the task of preventing mold growth in buildings appear daunting. However, it is essential to understand that these spores require substantial moisture to germinate and form active colonies.

The primary strategy for managing mold involves keeping indoor moisture levels below the threshold necessary for fungal proliferation. Fortunately, achieving this level of moisture control is quite feasible.

Control moisture by:

• Preventing condensation
• Routinely inspect for water leaking into your home, this includes plumbing leaks, roof leaks, leaky basements etc. Get leaks fixed immediately.
• Clean water damage and dry wet materials from flooding accidents within 24-48 hours.

Preventing Condensation:

Mold growth in homes often begins when high humidity results in condensation on cooler surfaces. Typical locations for this include the interior of exterior walls in closets or behind furniture, particularly during the winter heating season. In contrast, during hot and humid summer months, condensation frequently appears on cooler basement walls and floors.

To prevent condensation, consider these two strategies:

1. Raise Surface Temperatures – During winter, ensure that the interior surfaces of exterior walls, ceilings, and floors are properly insulated to keep them warm. Enhancing air circulation within the home can also increase surface temperatures. For example, keeping closet doors open during the winter heating season allows warm air to circulate into these spaces, helping maintain sufficient warmth to prevent condensation.

2. Reduce Indoor Moisture Levels – It is essential to expel moisture generated within the home to the outside. Ensure that clothes dryers are vented outdoors and install exhaust fans in kitchens and bathrooms to manage moisture from cooking and bathing. A useful guideline for reducing indoor moisture is to enhance ventilation when the outside air is cold and dry, and use dehumidifiers when the outdoor air is warm and humid.

By addressing both surface temperature and humidity levels, you can effectively minimize condensation and reduce the risk of mold developing in your home.

Undetected water leaks in plumbing systems, as well as leaking roofs or walls, can often lead to significant fungal growth within buildings.

It is essential to establish and adhere to a routine maintenance schedule for your home to identify leaks before they escalate into major issues. Conduct an inspection of your roof at least annually to check for any cracked or missing shingles; if your roof is older and showing signs of wear, more frequent checks are advisable.

Regularly inspect basements, crawlspaces, and areas under sinks for leaking pipes, and address any leaks promptly. It is crucial to prevent basements or crawlspaces from remaining wet or damp, even if they are not used as living areas or accessed frequently, as significant amounts of moisture can migrate from these spaces into your home’s living areas in vapor form.

Despite the best construction and maintenance efforts, flooding incidents can still occur. Events such as water leaks from a burst pipe or a severe rainstorm can rapidly inundate a house’s interior. In such cases, it is imperative to act swiftly to remove the water, clean affected areas, and ensure materials are thoroughly dried.

IMPORTANT: Water damage should be addressed within 24-48 hours to avoid mold problems.

Table 1 below offers detailed advice on responding to substantial water damage in your home.

TABLE 1: How to Cleanup Water Damage to Prevent Mold Growth

If mold has occured or materials have been wet for more than 48 hours, consult Table 2 guidelines below. Even if materials are dried within 48 hours, mold growth may have occured. Items may be tested by professionals if there is doubt. Note that further growth will not always occur after 48 hours; this is only a guideline.

These guidelines are for damage caused by clean water. If you know or suspect that the water source is contaminated with sewage, or chemical or biological pollutants, the Personal Protective Equipment (PPE) and containment are required by OSHA.

An experienced professional should be consulted if you and/or your remediators do not have expertise remediating in contaminated water situations. Do not use fans before determining that the water is clean or sanitary.

Relative Humidity and Condensation

Relative humidity is a measure that compares the current amount of water vapor in the air to the maximum amount the air can hold at a specific temperature. For instance, if a room’s temperature is 75 degrees and the relative humidity is at 40%, this indicates that the air contains 40% of its capacity for water vapor.

Should the air reach 100% saturation, any additional water vapor would condense into liquid form. It’s important to note that warmer air has a greater capacity for holding water vapor compared to cooler air.

For example, if the temperature in some areas of the room decreases from 75 to 60 degrees while the water vapor level remains constant, the relative humidity at 60 degrees would rise to 100%. The temperature at which vapor turns into liquid, known as the dew point temperature, is 60 degrees in this scenario.

Managing indoor relative humidity levels is crucial. Consider a home with an indoor temperature of 70 degrees and a relative humidity of 55%. Here, the dew point temperature is also 60 degrees, meaning that condensation will occur on surfaces at or below this temperature.

This is particularly concerning when outdoor temperatures are low, as poorly insulated homes or enclosed spaces like closets may have interior surfaces reaching or falling below 60 degrees. Conversely, if the relative humidity drops to 35%, the dew point lowers to 54 degrees, reducing the likelihood of condensation.

Understanding these dynamics is essential for maintaining a comfortable and moisture-free living environment.

What To Do if Mold Growth is Detected

If you discover mold actively growing in your home and it covers a small area, less than 10 square feet, you can typically manage the cleanup on your own. To determine the best method for cleaning the affected surfaces, please refer to the information provided in Table 2 below.

For areas exceeding 10 square feet, while self-cleanup remains possible, it is crucial to take necessary precautions to protect yourself and contain the area to prevent mold spores from spreading to unaffected parts of your home.

IMPORTANT: If you or your family members have allergies or asthma, it may be wise to seek professional assistance for mold remediation.

TABLE 2: Guidelines for Remediating Small Areas of Building Materials with Mold Growth Caused by Clean Water

Cleanup Methods*

Method #1:
Wet vacuum (in the case of porous materials, some mold spores/fragments will remain in the material but will not grow if the material is completely dried). Steam cleaning may be an alternative for carpets and some upholstered furniture.

Method #2:
Damp-wipe surfaces with plain water or with water and detergent solution (for finished wood surfaces you may want to use a wood floor cleaner). Scrub as needed.

Method #3:
High-efficiency particulate air (HEPA) vacuum after the materials has been thoroughtly dried. Dispose of the contents of the HEPA vacuum in well-sealed plastic bags.

Mold in hidden areas

Mold growth may not always be apparent to the naked eye. It can thrive in concealed areas such as within wall cavities behind gypsum wallboard or wood paneling, beneath wallpaper, or atop ceiling tiles.

Even if mold is not visibly present, there are several indicators that suggest its existence:

• A substantial mold presence in a hidden space is often accompanied by a noticeable odor. Mold typically emits a strong, distinctive “musty” smell.
• When high moisture levels are detected within a building, or if there are signs of water damage, it is reasonable to suspect mold growth.

Identifying moisture issues is generally straightforward; the air inside the building might feel damp and clammy. Additionally, heavily stained ceiling tiles or gypsum wallboard can serve as clear signs that water, likely from a plumbing or roof leak, is saturating building materials within wall or ceiling cavities.

To thoroughly assess concealed mold growth, it is often necessary to take down wall or ceiling coverings like wallpaper or ceiling tiles. In some instances, even the wall and ceiling boards must be removed to inspect the wood framing underneath. Since the extent of hidden mold can only be determined upon investigation, it is crucial to protect yourself in anticipation of potentially extensive mold presence. Therefore, wearing personal protective equipment (PPE) during your examination is highly recommended.

Should you have your home tested for mold?

Mold testing often necessitates the expertise of professionals, such as an industrial hygienist or Certified Master Home Inspector. Furthermore, there is no universally accepted standard for determining acceptable mold concentrations.

Identifying a mold issue typically does not require testing; if mold is not visible, it is usually detectable by its odor. Significant mold infestations emit volatile organic compounds that are easily noticeable by smell. Even when mold itself is not apparent, detecting moisture issues that lead to mold growth is relatively straightforward.

While this guide highlights various health concerns related to mold exposure, it is important to note that well-maintained homes that remain clean and dry generally do not support mold growth.

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