Except in structures where all of the incoming air is filtered and cleaned, there is never going to be a “mold-free” condition. Therefore, when checking a house for mold, the goal is to have the indoor mold condition equal to or lesser than the outdoor condition. Mold screening of the indoor and outdoor conditions determine if an indoor mold problem exists and what types of molds are growing indoors.
The health effects from mold exposure are very symptomatic, and vary from person to person. How the human system is affected by mold exposure is dependent upon what types of mold are growing and the condition of the person exposed to the mold.
There are approximately 100,000 genera of mold species known today, with approximately 80 genera suspected of causing some kind of illness. Only a fraction of the 80 genera are considered toxic. Molds are organized into three groups according to human responses: Allergenic, pathogenic and toxigenic. Allergenic molds do not usually produce life-threatening health effects, and are most likely to affect those who are already allergic or asthmatic. The human system responses to allergenic molds tend to be relatively mild, typically producing only scratchy throats and rashes. Pathogenic molds usually produce some type of infection. They can cause serious health effects in persons with suppressed immune systems, although a normal, healthy individual can probably resist infection by these organisms regardless of dose. In some cases, high exposure may cause hypersensitivity pneumonitis (an acute response to exposure to an organism). Some molds produce mycotoxins that can cause serious health effects in almost anybody. These agents have toxic effects ranging from short-term irritation to immunosuppression and possibly cancer. Therefore, when toxigenic molds are found further evaluation is recommended.
Airborne spores will eventually land and settle on a surface. Spores may or may not germinate immediately, but they are built for survival. The spores may lie dormant, waiting for the right condition for growth. The following conditions may be conducive for mold growth:
Moisture. When looking for the source of a mold growth, look for moisture. Spores can survive, germinate and reproduce in as little as 65% equilibrium relative humidity (water activity of 0.65).
CDC's National Center for Environmental Health
The National Institute of Environmental Health Sciences (NIEHS)
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