What is Mold?

Mold is a type of fungus. They are microscopic in size and can only be seen with the naked eye when they are growing in colonies. They are different from plants and algae in one major way. Fungi do not derive their energy through the process of photosynthesis. They have no chlorophyll. Photosynthesis is the process of converting light energy (the sun) into chemical energy (carbohydrates such as sucrose, glucose, or starch.) As a result, fungus does not need the light to grow and can be very happy growing in a dark, moist basement. Secondly, they must live on organic matter (plant or animal) to get their energy.

Growth

Mold can grow on virtually any substance as long as moisture, oxygen, and an organic source for food are present. Of these requirements, moisture is the most important.

Moisture can be in the form of high humidity, condensation, or water from a multitude of sources. With modern houses being built so air-tight, this helps on the utility bill but is not so helpful in combating moisture. Many household activities such as cooking, taking showers, or drying clothes indoors can raise the humidity level in the home. Condensation can also play a role. Water condenses when a surface is cooler than the air around it. We see this quite often on the mirror in the bathroom after a hot shower. Moisture can come from multiple sources for fungi to thrive on. Moisture must be controlled if mold growth is to be controlled. This moisture will also allow other common allergens to flourish such as those produced by dust mites and cockroaches.

Temperature is a factor but not an important one for growth. It may, however, favor one species over another. Some can thrive at high temperatures. Others may thrive in cooler temperatures and grow well on foods inside our refrigerators. They are a very hardy organism and extreme cold often only makes them go dormant rather than killing them. The ideal temperature for growth is the temperature that we keep our homes. Different species vary a lot in their tolerance to humidity and temperature.

Nutrients for a fungus are found virtually everywhere. They take carbohydrates, proteins, and other nutrients from animals, plants, or decaying matter. Carbon containing materials provide nutrients to fungi and they are abundant both outdoors and indoors. Many of the building materials that we use in construction provide the nutrients that fungi need to thrive.

Types of Mold

There are over 100,000 known species of fungi world wide. No one knows exactly how many species there are. Four of the commonly encountered allergen producing species are listed below.

Alternaria

• Grows indoors and a major cause of mold allergy symptoms
• Grows in thick colonies
• Cause fungal disease in agriculture and causes over 20% of agricultural spoilage

Aspergillus

• Prefers starchy foods such as bread and potatoes
• One of the more prolific airborne spore producers
• Can grow in places where there are not many nutrients
• Can be a health hazard to humans

Cladosporium

• Is one of the most common indoor and outdoor mold
• One of the most prolific airborne spore producers
• Rarely causes disease in humans
• A significant allergen and can affect people with asthma

Stachybotrys

• Prefers to grow on material rich in cellulose. Cellulose is found in paper, cardboard, and textiles made of cotton. It is also found in wide variety of building material.
• The most famous species from this genus is "black" or "toxic black mold"
• Known to produce mycotoxins which is a health hazard to humans

The above is a picture of Aspergillus using a staining technique. The magnification is at 562. Aspergillus is a fungus (or mold) that is very common in the environment. It is found in soil, on plants and in decaying plant matter. It is also found in household dust, building materials, and even in spices and some food items. There are lots of different types of Aspergillus.

Where is it Found?

A better question might be; where is it not found? It can grow on just about any surface where there is moisture. It grows in places that we can see and it loves to grow in places that we don’t see and don’t have access to (i.e., inside walls, the back side of wallpaper, or the underside of carpet).

Outdoors
Damp, shady areas are the most common places to find it growing. It is common to find it growing on rotting logs and leaves, dead and decaying organic matter, grasses, weeds, compost piles, and a long list of other surfaces, and especially where there is poor drainage.

Indoors
Indoors, mold is just as common and grows in the obvious and not so obvious places. Furthermore, it can grow all year long. Indoors, fungi prefer the dark, humid areas that can be found in many basements. It is common to find it growing on shower stalls, shower curtains, refrigerator gaskets and drip trays, humidifiers, air conditioning units, paint, ceiling tile, and a long list of other surfaces, especially where there is humidity.

The picture below shows mold growing around the bathroom tub. It is growing on the caulking that is suppose to be mildew resistant.

Conclusion

Mold and mildew is a very hardy organism. They do not require much for their existence. Once the conditions are right for their growth, they are very hard to eliminate.

The Good
Outdoors, they provide a vital function to our environment. By feeding on dead and decaying matter, the process of decomposition happens quicker. Fungi play a major role in breaking down of matter and recycling the nutrients back to enrich the soil.

The Bad
Indoors is not the place that we want fungi performing its role in nature. Furthermore, some species of fungi are toxic and a danger to humans. The decomposing process of fungi gradually damage building materials and furnishings.

The EPA has an excellent article about what you need to know about mold.

Go to the nasal allergies home page.

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