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Mold is a living organism, neither plant nor animal, but rather a fungus

Mold is found virtually everywhere, indoors and out. Mold’s primary function is to break down dead organic material and recycle nutrients back to the earth.  There are at least 1,000 varieties of molds common to the United States, and there are tens of thousands of different species worldwide.


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Molds multiply by producing microscopic spores, similar to the seeds produced by plants.  To understand how molds use spores to reproduce, picture a field of dandelions.  The dandelion forms seeds attached to white fluff.  This fluff is easily detached from the flower when stirred by a wind, an animal, or even you walking near it.  Once airborne, the seed lands in a new location where—with the right soil, sunlight, and water—it may grow into a new dandelion.


This is similar to how molds reproduce, on a much smaller scale.  Instead of seeds, molds produce and eject spores.  Like dandelion seeds, these spores can easily float through the air and can be carried great distances by even a gentle breeze.

When the spores become airborne and land in a new location—with the right food source and moisture—they may form a new mold growth. The problem for us mammals is that, between the ejection of the spore and its growth into a new mold, plenty of spores are floating around in the air, both inside and outside our houses.

Unless you live in a bubble, inhaling spores is as inevitable as inhaling pollen during certain times of the year.  Many people suffer from seasonal allergies or “hay fever.”  This sensitivity to pollen or mold spores triggers a reaction from your immune system, causing an allergic reaction.


The number of mold spores suspended in the air fluctuates a great deal, season to season.  In temperate climates, outdoor spore counts often number in the thousands during the summer but may go down to zero in mid-winter, when everything is snow-covered.  Inside your house, mold spores are always present.  Doubt it?  Leave a piece of bread on the kitchen counter for a week and see what grows.

Mold becomes more of a problem when it starts growing inside homes and occupied spaces.  Modern construction techniques, meant to improve comfort and energy conservation, can actually increase your exposure.  As homes become increasingly airtight, fresh air exchanges are reduced, leading to a potential buildup of excess moisture and mold growth.  In addition, modern construction materials (drywall instead of plaster, for example) are often more conducive to mold growth.

Moisture (water or even elevated humidity) is the crucial ingredient for mold growth.  Mold can grow on just about any surface, but it prefers to feed on porous, organic materials—things that were once alive themselves, like plants or trees for example.  Certain molds are particularly fond of cellulose materials such as wood, drywall, or ceiling tiles, and can potentially cause structural problems.

Not all types of molds are toxic. However, many common molds can create health problems; and, just like sensitivity to pollen, some people are more sensitive than others.  Infants, children, the elderly, pregnant women, immune-compromised people, and people with respiratory conditions all may have a greater risk for adverse health effects to mold.  Beyond that, it’s just luck of the draw: Some people are more sensitive to molds than others.  Mold plays an essential role in the ecosystem, and mold spores are around us all the time; however, visible mold growth in a building may increase your exposure, is a potential health hazard, and should therefore be removed.

In future articles, I will discuss the origins of the phrase “black mold” and how it helped raise awareness of indoor air quality, as well as how to diagnose and eliminate indoor mold problems.

By Dedicated Environmental | February 7th, 2018


“Do I have black mold?” the homeowner asked—a question I have been asked repeatedly over the last 15 years.  What she was really asking, although she may not have known it, was “Is this Stachybotrys?”  Stachybotrys became commonly known as “black mold” in the 1990s, when a rather publicized case gained national attention.  In this case, a number of infant deaths in Cleveland were attributed to exposure to Stachybotrys. 


In November 1994, Dr. Dorr Dearborn of the Rainbow Babies and Children’s Hospital treated several infants for unexplained pulmonary hemosiderosis.  The babies’ lungs were bleeding, a condition so rare that it usually affects only one in a million children.  Yet several Cleveland cases had been reported in a matter of days.  In fact, doctors in 24 states had reported 79 unexplained bleeding-lung cases in infants; and thirty of these were in Cleveland—including several infants who had died.  Most of the Cleveland cases were on the east side of the city, in a lower-income neighborhood. 

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Stachybotrys has a slimy, black appearance when wet and it grows on cellulose materials such as cardboard, wood, paper, or cloth.  Unlike other molds, some of which can thrive on elevated humidity, Stachybotrys needs a direct water source.  Indeed, just months before Dr. Dearborn began observing the unusually-high number of cases in Cleveland, a heavy rainstorm had flooded many homes in the area. 


As these cases came to light, Dr. Ruth A. Etzel, head of the CDC’s Air Pollution and Respiratory Health Branch, conducted a study involving 40 Cleveland-area infants—10 sick and 30 healthy infants as a basis for comparison.  All the babies lived in the same area, and the study began to show a correlation between the disease and exposure to Stachybotrys chartarum (also called Stachybotrys atra). 


Some strains of Stachybotrys produce toxins that are highly dangerous to humans and have been used to produce chemical and biological weapons.  Mold spores and toxins can become airborne and, once inhaled, may attack the immune system.  Studies have shown that adults who have had chronic exposure to Stachybotrys have reported a variety of maladies, including flu-like symptoms, skin irritation, and fatigue.  Dr. Etzel’s investigation also cited evidence that Stachybotrys had caused hemorrhaging in farm animals in Europe.  The effect on human infants, as suggested by the Cleveland study, seems potentially severe.

During the study, the county coroner reviewed all 172 infant deaths between 1993 and 1995.  Using tissue samples collected before the infants had been buried, doctors found that six of the 117 deaths previously attributed to Sudden Infant Death Syndrome were more likely caused by mold exposure.  All six had lived on Cleveland’s east side. 

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Ultimately, examinations of the Cleveland homes found Stachybotrys in several of them.  Air testing of all the case and control homes revealed evidence of black mold near furnaces, which investigators believed may have distributed the spores throughout the houses of the case infants.  Heavy rains and ongoing plumbing problems contributed to water damage in some of the case homes, creating the right environment for Stachybotrys growth. All case infants lived in homes older than sixty years, all of which had recent water damage.  Investigators found that the affected infants were more likely to live in homes with larger quantities of Stachybotrys and other molds than were the control infants.  The CDC report did not detail exactly how the mold hurt infants; but Dr. Dearborn theorized that the mold produced airborne toxins that weakened tiny blood 

vessels in the infants, as their lungs were developing.  The effect of these toxins may have been exacerbated by secondhand smoke or other illnesses, setting off the attack.

In subsequent years, some of the study’s conclusions were questioned, but by no one providing better answers.  By the time the CDC published its results in 1997, the public had become aware of the dangers of “black mold.” 


“Black mold.”  Even the name conjures up a certain amount of intrinsic dread.  In reality, any number of mold varieties—or colors—can affect air quality and create potential health issues for humans.  While increased awareness of Stachybotrys may have been accompanied by some amount of “black mold” hysteria, it also served to raise public awareness that mold, left unchecked in the home, can be harmful to its occupants; and that awareness leads to a better understanding of how to deal with the problem. 


 In upcoming articles, I will discuss the methods to deal with the problem: how to identify treat, eliminate, and avoid mold growth in the home. 


Not all types of molds are toxic; however, many molds can create health problems and some people are more sensitive to mold exposure than others.  Infants, children, the elderly, surgery patients, immune-compromised people, pregnant women, and persons with respiratory conditions all appear to have greater risk for adverse reactions to mold.  Many health symptoms have been commonly linked to mold exposure, including sneezing, coughing, runny nose, nasal congestion, itchy or watery eyes, skin rashes, sinus headaches, difficulty breathing, and a host of others.  Allergic reactions are the mostly commonly-reported symptoms.


Mold is a fungus and needs a few things to grow in your house or building.  Food, moisture, warmth, and oxygen are the main requirements.  Moisture, in particular, is the most crucial ingredient.  A number of molds aren’t all that finicky, easily growing in areas with elevated humidity and an organic food source.  Even just slightly- or intermittently-elevated humidity can sometimes be enough.  Humidity lingering above 50% or 60% for too long may invite fungal growth.  Lack of airflow seems to foster elevated humidity, especially in areas like attics, basement closets, or closed areas (such as a bathroom vanity) where condensation might be present. 


Many homeowners report smelling a musty odor somewhere in their houses.  Sometimes the smell is more noticeable after a rain.  This odor may be a byproduct of mold actively feeding into something.  When the humidity goes up, the mold starts feeding.  When some molds feed, they release gases that you can smell.  When the area dries up or the humidity decreases, the mold may stop feeding or go dormant—just waiting for the next time it is provided with the right growing conditions.  In this way, it is not unusual for a homeowner to notice the smell stronger some days (or seasons) and almost imperceptible others. 

Different molds have very different appearances.  A number of molds appear as a powder, growing on just about any surface, but particularly on porous, organic surfaces.  Certain molds are especially fond of cellulose materials such as wood, drywall, paper, cardboard, or ceiling tiles, and can cause structural problems.  These molds can be just about any color and, as mentioned above, can thrive on a direct water source or merely elevated humidity.  They are often visible to the naked eye and can sometimes be detected growing on surfaces by holding a flashlight at certain angles.

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Other molds, such as Stachybotrys, will typically only grow in areas that have had a direct water source.  Stachybotrys often appears as a black, slimy mold. Still other molds may appear as a mushroom or pasta-looking growth.

The best way to determine whether you have an indoor air quality problem is to hire a mold inspector.  A mold inspector is typically quite affordable; and a trained inspector not only knows where to look and what to look for, but also has the tools to help find hidden problems.  For example, in a finished basement, what you see is not necessarily what you get.  Drywall, plaster, or wood paneling hung on foundation walls can often foster—and hide—fungal growth.  The tight space (insufficient airflow) between the finished wall (organic surface) and the foundation (humidity source) is just the recipe for mold.  Humidity readings taken during an inspection may reveal humidity conducive to mold growth.  Moisture readings taken on the surface of a wall may reveal previously-unknown water problems behind the surface.  A surface sample can help uncover the identity of a mysterious discoloration.  And a single air sample taken inside a house will reveal precisely what you are breathing on a daily basis. 

While not all molds are considered toxic, different people have different sensitivities.  Many molds can create health problems for people—especially when we are closed up in buildings that have mold problems.  The analysis of an experienced inspector can help determine what issues exist in the house and how to resolve them. 


In upcoming articles, I will discuss how to prevent mold growth in your home or building.



Some years ago, I was inspecting a local theater that had flooded.  The water had come from above (a fire suppression system), during a period when the building was vacant.  By the time the flooding was discovered, the mess had sat for some time and the entire building was covered in mold.


The theater had been in operation for many decades and had an extensive costume collection.  Sadly, every stitch of clothing was ruined by water damage and fungal growth.  I remember walking through the costume shops with a renewed respect for the devastation that can be caused by water and the mold growth that ensues. 

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While surveying the rooms of costumes, I came upon a large, plastic tote with its lid snapped tightly in place.  As water rolled off the top, I removed the lid to behold the single item inside—a white wedding gown.  I lifted the gown out of the container and gazed at it.  What struck me then and remains in my memory today was the condition of the gown.  It was pristine, completely untouched by the devastation all around it.  I stood in the center of a room completely covered in the blackness of unchecked mold, holding a crisp, white wedding gown. 

The moral of the story: Plastic totes save lives.  Okay, maybe not lives; but at least the lives of whatever we want to store.  Even a flood and the mold growth that followed didn’t disturb the sanctity of that plastic tote.  That same week, I bought as many plastic totes as I could lay my hands on and transferred items in my own basement from cardboard boxes to the plastic totes.  If similar calamity strikes me, at least I won’t lose everything. 


Of course, the best way to avoid mold growth in your home is to avoid the conditions that create it in the first place; and the best way to do that, simply put, is to REDUCE MOISTURE and INCREASE AIRFLOW.  There are several specific things you can do to decrease the odds of indoor mold growth:

1. Reduce indoor humidity.  The EPA recommends keeping indoor humidity below 50-60%, as humidity below 50% is not conducive to fungal growth.  In the spring, summer, and fall, use a dehumidifier in the basement to ensure that relative humidity stays below this cutoff.  A self-draining dehumidifier (using a hose to drip into a floor drain) with its humidistat set for 45% makes a relatively maintenance-free way to keep humidity-loving molds at bay.

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2. Repair/eliminate all leaks.  This may include small issues such as a leaking A/C unit, furnace condensate line, or dripping pipe to larger issues like ongoing plumbing leaks, clogged gutters or downspouts, roof or chimney leaks, or foundation water intrusion.  In the event of a known water event, wet materials that are porous and organic should be dried out within 24-48 hours.  Mold needs moisture to thrive, so eliminating leak sources is essential.  

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3. Cover dirt floors in crawlspaces, using 6-mil poly sheeting that you can find at any home improvement store.  Overlap any seams and tape them, if desired.  Staking the plastic into the dirt with landscape fabric stakes can help keep the sheeting in place the next time someone has to work in the crawlspace to work on plumbing, cables, etc.

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4. Improve airflow.  Airflow is important in closed spaces where humidity may linger, such as closets, closed basement rooms, and attics.  Attics, in particular, should be designed to facilitate airflow.  These days, builders and roofers prefer a combination of soffit vents at the eaves and a ridge vent at the peak of the roof, as shown in this diagram.  The soffit vents allow fresh air to flow into the attic while the ridge vent allows air to flow out.  Older homes may have end vents and/or pot vents on the roof.  In any case, all attic vents should be unobstructed to facilitate the flow of air.  If all else fails, an electric exhaust fan may be added to remove hot, humid air from an attic.  Door vents may be desirable on basement closets.  When it comes to preventing mold growth, more airflow is best.

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5. Ensure that mechanical vents are properly exhausted.  Dryer vents, bathroom vents, and stove hoods should all exhaust outside the house.  A vent pumping warm, steamy air into a living space or attic will ultimately create an environment conducive to mold growth.  Many an attic is full of mold because of an improperly-vented bathroom fan, as is illustrated by this photo.  Although now correctly exhausted to the outdoors (in this case, out the roof), the bathroom fan originally exhausted directly into this attic, creating the white fungal growth pictured

Plastic totes may be a great way to protect treasured items from calamity but, as the old saying goes, an ounce of prevention is worth a pound of cure.  Decreasing indoor humidity and increasing airflow can help head off problems before they start.


Do I have black mold
how to detect and prevent
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