Leighton Associates


A growing body of evidence indicates the air we breathe in our homes and offices contains more pollutants and dangerous toxins than the outdoor air in large, industrialized cities! This is a serious matter because the average person spends about 90 percent of his or her time indoors. What is polluting indoor air?

Indoor pollutants include radon, combustion products, organic gases, lead, asbestos, and biological contaminants. Biological pollutants (or bioarosols) are a by-product of plant and animal material. Some, like pollen, are generated outdoors and brought inside while others, such as mold, animal dander, and insect excrement can be generated indoors. These microscopic particles remain airborne and are inhaled when we breathe. This web site is dedicated to one of the most common and troubling biological contaminants--mold.

What Causes Mold?

Mold, which is a type of fungi, has a purpose in nature--it causes wood and other dead natural materials to decompose. Without mold, dead trees, plants and leaves would never decay. Mold serves an important ecological role outdoors but these attributes are not desirable or beneficial indoors.

In order for mold to grow, several conditions must exist. Mold spores must be present, there must be a source of food (such as cellulose or wood products), and there must be water or high moisture present. Mold spores and cellulose exist naturally in most building products (e.g. wallboard, ceiling tile, carpet, wood flooring, etc.). So, when these materials become wet or damp, mold can grow.

Mold can appear indoors wherever there is flooding, leaking pipes or roofs, standing water, or moist surfaces. You may find mold in:

  • Places where water collects such as dehumidifiers, air conditioner drip trays, and refrigerator collection pans.

  • Highly humid areas such as bathrooms, laundry rooms, basements and crawlspaces.

  • Places where moisture can enter the building due to incorrectly installed vapor barriers, insulation materials, windows, etc..

  • Areas subject to direct water entry due to leaking pipes or roofs, poor drainage, and floods from natural causes or fire extinguishment.

However, signs of mold and its causes are not always obvious. Sometimes people experience vague, persistent symptoms when mold growth is not visible. It is not uncommon to discover mold growing behind walls, under floors or above ceilings. In this way it pollutes the air, unbeknownst to building occupants. Indoor air testing is usually the best way to detect spores coming from these hidden sources.

Mold & Mycotoxins

Three common molds found indoors are Aspergillus, Penicillium and Stachybotrys. Of particular concern, is Stachybotrys, a slimy, dark green mold. Stachybotrys has been blamed for infant deaths and severe health problems in adults who breathe its particles. During its growth process, Stachybotrys produces tricothosine mycotoxins, which are some of the most potent toxic chemicals known to man. In fact, at one time, the U.S. Government considered using these mycotoxins as biological warfare agents!

Mycotoxins are used by mold to protect its turf; that is, to kill other fungi. Penicillin is a well known mycotoxin produced by the fungi Penicillium. It is used to man's benefit as an antibiotic to kill infections. People have varying sensitivity to mycotoxins, causing some individuals to have allergic reactions to them. For example, some people are allergic to penicillin.

Other molds are allergens as well, which is why people may experience the onset or exacerbation of allergy symptoms when mold is present. As you might expect, viable mold spores can grow, increasing the production of mycotoxins. But non viable spores can also cause allergic reactions even though they are "dead". These dead spores can remain biologically active for years after mold growth has ended!

At the very least, mold growth is a nuisance, in terms of its unpleasant appearance and odor. At its worst, mold can cause serious health problems and irreparable damage to buildings and property.


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