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By Nancy B. Solomon, AIA

Biology 101

To prevent mold, architects should first understand something about the creature. Molds are a type of fungus. Fungi occupy two kingdoms of the seven cited in the current classification system of biological organisms. Unlike organisms in the animal kingdom, which digest food internally, fungi secrete enzymes into the environment to break down material into smaller components that they can then absorb. This process serves the extremely important role of cleansing and recycling elements in nature.

The fuzzy-looking part of mold is called the mycelium, which is made up of many slender cells called hyphae. Digestion occurs at the ends of the hyphae. As the mold grows, the hyphae must continue to multiply and reach further out to gather more nutrients to satisfy the ever-larger organism. Different types of molds digest different types of foods. Unfortunately for the building industry, many molds like the cellulose in wood products; through this process, they can discolor and ultimately destroy the host material.

Molds reproduce through spores, which fly through the air with the greatest of ease. If conditions at landing are right, the spores will germinate and fungal growth will begin. Molds release microbial volatile organic compounds, which cause the musty smell, and produce allergens and, under certain conditions, toxins. The allergens and toxins are not airborne themselves but can be carried in flight with the spores. It is these allergens and toxins that are the potential medical culprits.

Spores, which are microscopic, are found virtually everywhere. There is no cost-effective way of removing them from all buildings. To germinate, they need oxygen, food, an acceptable temperature, and sufficient water. The typical indoor environment provides all these factors except possibly one: Mold requires a higher quantity of moisture (in the order of 70 percent relative humidity or higher) than is comfortable to humans (20 to 60 percent relative humidity). So, the building industry’s only viable defense against mold is moisture control.

 

Summary of Findings Regarding Association Between Health Outcomes and Exposure to Damp Indoor Environments Sufficient Evidence of an Association Upper respiratory (nasal and throat) tract symptoms Cough Wheeze Asthma symptoms in sensitized persons Limited or Suggestive Evidence of an Association Dyspnea (shortness of breath) Lower respiratory illness in otherwise healthy children Asthma development Inadequate or Insufficient Evidence to Determine Whether an Association Exists Airflow obstruction (in otherwise healthy persons) Mucous membrane irritation syndrome Chronic obstructive pulmonary disease Inhalation fevers (nonoccupational exposures) Lower respiratory illness in otherwise healthy adults Acute idiopathic pulmonary hemorrhage in infants Skin symptoms Gastrointestinal tract problems Fatigue Neuropsychiatric symptoms Cancer Reproductive effects Rheumatologic and other immune diseases