Mold and mildew have been around since the beginning of creation. So, why is it, that in the last few years there has been so much fuss about mold?
To begin, molds are a part of the Kingdom Fungi. This Kingdom is divided into yeasts, mushrooms and molds. Mildew is a type of mold.
Molds are ubiquitous, meaning that they are everywhere. Unless you are in a sterile environment, you can sample the air or the surface of anything and always find molds present. You would generally expect to see the same types of molds, in equal or fewer numbers, in the inside of a home or building as you would see in the outside air.
Since Molds Have Been Around Forever, Why Is It Just Now
Becoming a Problem?
Mold problems have been around for a long time. In the Bible, at Leviticus the 14th chapter, there is a procedure for the handling of the leprosy of the wall. The Hebrew word used in this text is tsara’ath, which, according to Strong’s Exhaustive Concordance, can be translated as mold when used in conjunction with clothing or a building. That makes the first written mold remediation protocol in recorded history over 3500 years old. The High Priest was the first environmental consultant and his visual inspection to determine reoccupancy was the first environmental clearance.
The following is a generalization of how changes in building design and construction have contributed to the increased number of mold problems in recent years. In the 1950’s, houses were not as well insulated as they are today and therefore were drafty. In those areas of the country where the summers are hot, we began installing wall air conditioners to make the indoor environment more comfortable. In the 60’s we began installing central heat and air. In the 70’s we had an energy crisis that forced most of us to find ways to conserve energy. One way was to insure that the building envelope was air tight and insulated. By doing this, we were able to minimize the heat loss or gain through the building’s exterior walls and control airflow to some degree. While this saved energy, it also reduced the building’s ability to dry out when it got wet. In the 80’s there were an increasing percentage of homes and buildings that were designed and built for energy conservation. In the late 80’s we started hearing about SBS (sick building syndrome) related to office buildings that lacked operable windows. By the late 80’s a connection was being drawn between mold and tight building construction and sometimes-poor construction. In the 90’s the media began catching on to the fact that some homes and buildings were making people sick. Mold wasn’t the only culprit in SBS, but was one of the many IAQ problems that developed.
Most fungi are saprophytic, which means that they feed upon dead, decaying matter. Some are parasitic in that they derive their nutrition from living organisms. The saprophytic fungi help to prevent an inordinate amount of debris from accumulating and covering the surface of the planet.
There is always a food source available in the indoor environment. Molds will feed on many building materials such as wallpaper, drywall, paint, some carpets, adhesives, wood, fabrics, paper products and other organic materials. No doubt you have seen mold grow on the tile in your shower stall or shower curtain. It is not feeding on the tile or plastic curtain, but on the biofilm that is on the surface. Molds are microscopic and until a large enough mass has accumulated they can only be seen with the aid of a microscope. Because they are so small, even a very thin film of dust and debris will yield an abundance of food.
Molds cannot grow
without moisture. First, moisture is required in order for the mold spore (the
reproductive seed-like structure of many molds) to germinate. After germination
the mold’s hyphae (or root like structures) secrete digestive enzymes that
break down organic material. Moisture is necessary for the enzymes to be
effective. Then the hyphae absorb the nutrients by “bathing” in the digested mixture.
Although fungi also need oxygen, removing moisture is the most effective method
for halting growth.
Indoor
environment (food) + moisture = mold growth
Indoor
environment (food) – moisture = no mold growth
When the equilibrium relative humidity (ERH) of a surface is above 70% some mold spores can begin to germinate. There are a few molds that can start to germinate at an even lower ERH. Depending on the species of molds, germination can take place in as little as 4 to 12 hours. After germination occurs, it takes time for the mold to develop, create spores and begin to colonize. Colonization can occur in ~ 1-2 days in the case of Mucor sp. or Rhizopus sp., ~ 2-3 days in the case of Aspergillus sp. and Penicillium sp., and ~ 8-12 days in the case of Stachybotrys.
When molds are allowed to grow in wet-damp indoor environments, there is a likelihood that they can develop into enough volume to cause both damage to building materials and harm to some people. Whether or not someone will have an adverse reaction to mold exposure depends on many factors that include, but are not limited to: 1) the amount of molds present, 2) the type of molds present, 3) whether there is a pathway from where the molds are located to the person, 4) how long the exposure may take place and 5) how sensitive the individual may be to the exposure.
As molds feed on their food source, they produce a byproduct of digestion that results in that moldy, musty odor which is a MVOC (microbial volatile organic compound). When you smell that odor, you know that there is, or recently has been, a wet-damp environment that has allowed mold to start growing. According to the American Conference of Governmental Industrial Hygienists, “At present, the specific contribution of MVOCs to building related health problems has not been studied.”
Fungi produce agents
that can be toxic to humans depending upon exposure. These agents include, but are not limited to, mycotoxins,
antibiotics and glucans. There are hundreds of mycotoxins. They are usually
cytotoxic, which means that they cause cell disruption and interfere with
essential cellular processes. Some mycotoxins are considered carcinogens such
as Aflatoxin produced by Aspergillus flavus. Others may result in
adverse health effects to the nervous system, the liver, kidneys, lungs, blood,
skin and other body parts.
Examples of toxigenic
fungi
Aspergillus nidulans Penicillium
chrysogenum
Aspergillus versicolor Penicillium
expansum
Aspergillus fumigatus Penicillium
verrucosum
Aspergillus flavus Penicillium
viridicatum
Fusarium Stachybotrys chartarum (atra)
Remember, killing
spores does not eliminate the potential for allergy or sensitization.
Mycotoxins can exist on dead spores and MVOCs can linger in building materials.
Exposure and Sensitivity
Exposure and
sensitivity are difficult subjects to explain in one short paragraph. It's like
asking how much sun it takes to cause sunburn. It varies from person to person.
For some it takes very little exposure to cause an adverse reaction. I recently
read an article about a little girl that could not be in direct sunlight. To do
so would result in severe blistering. On the other hand, some people can be in
the sun for long periods of time without any adverse reaction. Also, when
someone is severely sunburned, he or she becomes more sensitive; in other
words, it takes less exposure the next time to create the same reaction.
Likewise, exposure to molds can make someone more sensitive to it. Once a
person is removed from the exposure, the reactions tend to diminish. While sun
is primarily a dermal exposure issue with a potential for heat stress, adverse
reactions to mold exposure can be dermal or internal due to ingestion or
respiration. As a general rule, when you see molds, the moisture problem needs
to be resolved and the molds removed.
Since fungal fragments
and spores are often airborne, individuals with genetic predisposition to
allergies and asthma, and that are exposed to these fungal parts, may react
adversely. Other individuals can become sensitized following exposure and may
gradually develop health symptoms over a long term. Antibodies can develop
against a specific allergen. Allergy is the most common symptom associated with
indoor molds. Specific physiologic responses occur which can result in watery
eyes, runny nose and sneezing, itching, coughing, headaches, fatigue and
wheezing. Even people who do not meet the criteria for an allergic diagnosis
may still experience burning eyes, runny nose, scratchy throat, and red or
itchy skin. Fungi are considered irritants in these cases.
Serious
Illness
Fungi can also cause serious infections and systemic
diseases. Athlete’s foot is a common example of fungal infection. Other
conditions resulting from infection include Aspergillosis, brain
abscesses and fungal cysts. Some fungi can also cause potentially fatal
systemic diseases such as histoplasmosis, blastomycosis and coccidiomycosis.
Immunocompromised individuals are more likely to develop serious fungal
infections than healthy individuals.
According to the EPA, “The term "sick building syndrome" (SBS) is used to describe situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building, but no specific illness or cause can be identified. The complaints may be localized in a particular room or zone, or may be widespread throughout the building. In contrast, the term "building related illness" (BRI) is used when symptoms of diagnosable illness are identified and can be attributed directly to airborne building contaminants”
Health effects generally fall into four categories. These four categories are allergy, infection, irritation (mucous membrane and sensory), and toxicity
Types of
Fungi
Acremonium
This mold is
commonly found in soil and on dead plant material. Indoors it grows on wet
building materials like drywall ceiling tiles and building paper. Acremonium
should be considered allergenic and may be a pathogen for immunocompromised
individuals.
Alternaria
Commonly
found in outdoor air, on many kinds of plants and foodstuffs and prefers
rotting farmland manure. It may be resistant to fungicides. Alternaria
is considered an occasional contaminant of water damaged building materials
which contain cellulose. Although Alternaria is a notable source of
fungal allergy, pathogenic infections are also reported infrequently.
Aspergillus
There are a wide variety of
species of Aspergillus. Some are considered opportunistic pathogens and
may cause pulmonary infections. Some members also produce mycotoxins and have been
implicated in causing allergic reactions and hypersensitivity pneumonitis. Aspergillus
type organisms are some of the first fungi to grow on water-damaged materials
and are frequently found in water-damaged structures. Although they are
commonly found in the outdoor environment, the outdoor frequency is generally
considered low.
Aureobasidium
This
yeast-like fungus is commonly found on caulk or damp window frames in
bathrooms. Aureobasidium may be pink or black in color. Although it
seldom causes infections, it can be allergenic. This is one type of mold that
is a type of mildew. It will grow in cooler climates and along with Cladosporium
is commonly found growing on siding.
Basidiospores
Frequently
associated with dry rot, Basidiomycetes are primarily mushrooms,
toadstools, puffballs, rusts and smuts. High levels of these spores can
contribute to allergies in indoor environments. Poria incrassata is a
particularly destructive fungal organism that falls into this classification. Poria
has resulted in the collapse of severely infested buildings.
Botrytis
Most
commonly associated with plants, Botrytis can cause allergic asthma
after indoor exposure. High levels are likely to be found in greenhouses or
other indoor areas with high humidity and large numbers of plants.
Ceratocystis/Ophiostoma
This is a very common plant pathogen that is frequently found on lumber
in lumber yards and is built into most homes. It has not been well studied and
has not been reported to be pathogenic or a producer of mycotoxins or
allergens.
Chaetomium
Commonly
found on deteriorating wood products, Chaetomium frequently emits a
musty odor and is frequently found on water-damaged drywall. Its health effects
have not been well studied, however some rare compounds have on occasion been
identified as mutagenic.
Cladosporium
Cladosporium is the genera most frequently
encountered in both outdoor and indoor air. It is frequently found in elevated
levels in water-damaged environments. Some species may be resistant to certain
types of treated lumber.
Epicoccum
A secondary
invader of plant materials, Epicoccum can grow at higher temperatures
than many fungi, allowing it to be a human skin pathogen. Colonies produce a
wide variety of colors depending on the food source. Although it may be
isolated from water damaged building materials, it is generally thought of as a
typical outdoor organism.
Fusarium
Found in
soils and on plants worldwide, Fusarium can invade corn and barley and
produce toxins at lower temperatures than many fungi. Fusarium has
affected water-damaged carpets and a variety of other building materials, and
can cause infection in immunocompromised individuals. Its spores are typically
slimy and may be difficult to isolated from air samples. It has also been
implicated in exacerbation of allergies and asthma and may produce mycotoxins.
Mucor
This mold is
found worldwide and is frequently present in air samples. Mucor commonly
grows on dung and moist hay. It is fast growing opportunistic and may cause
rare infection in immunocompromised individuals. It is considered a mild
allergen.
Penicillium
Penicillium species are common contaminants on various substances. This organism
causes food spoilage, colonizes leather objects and is an indicator organism
for dampness indoors. Some species are known to produce mycotoxins. The health
of occupants may be adversely affected in an environment that has an
amplification of Penicillium. Penicillium
is one of the first fungi to grow on water-damaged materials and has been
implicated in causing allergic reactions and hypersensitivity pneumonitis. It
commonly produces a strong musty odor.
Pithomyces
Found in
decaying wood, soil, and plant material, Pithomyces is not known to
cause infections or major health problems in humans. It has been found growing
on paper but is not commonly found growing indoors.
Rhizopus
Frequently
found in house dust, soil, fruits, nuts, and seeds, Rhizopus often grows
in fruit and vegetable garbage, or in forgotten leftover food. Exposure to
large numbers of Rhizopus spores has reportedly caused respiratory
complications. Rhizopus can be an allergen and opportunistic pathogen
for immunocompromised individuals, especially those with diabetic ketoacidosis,
malnutrition, or severe burns.
Stachybotrys chartarum
Stachybotrys
grows well on extremely wet building materials containing cellulose that have
remained wet for more than a week. It produces mycotoxins that can irritate
skin and mucous membranes. One potent mycotoxin produced by Stachybotrys
is called satratoxin; it is also toxic when inhaled. Extreme care should be
taken when this organism is amplified indoors.
Trichoderma
One of the
most widespread soil fungi, Trichoderma grows in carpet, on unglazed
ceramics, and on paper in damp homes. Some species produce metabolites related
to trichothecenes, which can be toxic and may cause symptoms like those
associated with Stachybotrys chartarum. It is also an allergen and may
infect immunocompromised individuals.
Ulocladium
Isolated
from soil, wood, and decaying plant material, Ulocladium grows on very
wet walls and particleboard. Because of its high water requirements it is considered
an excellent indicator of water damage. This genera is allergenic, contributing
to the allergy load especially in those with Alternaria allergy.
Wallemia
Found
worldwide in house dust, air samples, dry foodstuffs and soil. Wallemia
attacks materials with low water activity, is an allergen and may produce
mycotoxins. It is known to grow on materials with high salt content.