Mold​—Friend and Foe!


Some molds save lives; others kill. Some add to the flavor of cheeses and wines; others make food poisonous. Some grow on logs; others infest bathrooms and books. In fact, molds are everywhere​—spores might even be passing through your nostrils as you read this sentence.

IF YOU doubt that mold is all around us, just leave a slice of bread lying around, even in the refrigerator. Before long it will develop a fuzzy coat​—mold!

What Is Mold?

Molds belong to the Fungi kingdom, which boasts over 100,000 species, including mildews, mushrooms, plant rusts, and yeasts. Only about 100 funguses are known to cause disease in humans and animals. Many others play a vital role in the food chain​—decomposing dead organic matter and thereby recycling essential elements in a form that plants can use. Still others work in symbiotic relationships with plants, helping them to absorb nutrients from the soil. And some are parasites.

Mold begins life as a microscopic spore carried by air currents. If the spore lands on a suitable food source that has, among other things, the right temperature and moisture level, the spore will germinate, forming threadlike cells called hyphae. When hyphae form a colony, the fluffy, tangled mass is called a mycelium, which is the visible mold. Mold may also resemble dirt or a stain, such as when it forms on the grout between bathroom tiles.

Mold is a master at reproduction. In the common bread mold, Rhizopus stolonifer, the tiny black dots are the spore bodies, or sporangia. Just one dot contains upwards of 50,000 spores, each of which can produce hundreds of millions of new spores in a matter of days! And given the right conditions, mold will grow just as well on a book, a boot, or wallpaper as on a log in a forest.

How do molds “eat”? Unlike animals and humans, who eat first and then absorb their food through digestion, molds often reverse the process. When organic molecules are too large or complex for molds to eat, they exude digestive enzymes that break down the molecules into more simple units, which they then absorb. Also, since molds cannot move around to search for food, they must live in their food.

Molds can produce toxic substances called mycotoxins, which may cause adverse reactions in  both humans and animals. Exposure may occur through inhalation, ingestion, or contact with the skin. But the story is not all bad, for mold has some very useful properties.

The Friendly Face of Mold

In 1928 scientist Alexander Fleming observed by accident the germicidal power of green mold. Later identified as Penicillium notatum, the mold proved to be lethal to bacteria but harmless to humans and animals. This find led to the development of penicillin, termed “the single greatest lifesaver of modern medicine.” For their work, Fleming and fellow researchers Howard Florey and Ernst Chain were awarded the Nobel Prize for medicine in 1945. Since then, mold has furnished a number of other medicinal substances, including drugs for treating blood clots, migraine headaches, and Parkinson’s disease.

Mold has also been a blessing to the palate. Take cheese, for example. Did you know that Brie, Camembert, Danish blue, Gorgonzola, Roquefort, and Stilton owe their distinct flavors to certain species of the mold Penicillium? Likewise, salami, soy sauce, and beer owe much to mold.

The same is true of wine. When certain grapes are harvested at the correct time and with a suitable measure of fungal growth on each bunch, they can be used to produce exquisite dessert wines. The mold Botrytis cinerea, or “noble rot,” acts on the sugars in the grapes, enhancing the flavor. In the wine cellar, the mold Cladosporium cellare adds a final touch during the maturing process. To paraphrase an adage of Hungarian winegrowers: ‘A noble mold spells a good wine.’

When Mold Becomes a Foe

The harmful traits of certain molds also have a long history. In the sixth century B.C.E., the Assyrians used the mold Claviceps purpurea to poison the wells of their enemies​—an ancient form of biological warfare. In the Middle Ages, this same mold, which sometimes forms on rye, gave many people epileptic fits, painful burning sensations, gangrene, and hallucinations. Now called ergotism, the disease was dubbed St. Anthony’s fire because many victims, hoping for a miraculous cure, made a pilgrimage to the shrine of St. Anthony in France.

The strongest carcinogenic (cancer causing) substance known is aflatoxin​—a toxin produced by molds. In one Asian country, 20,000 deaths a year are attributed to aflatoxin.  This lethal compound has been used in modern biological weapons.

In everyday life, however, the symptoms of exposure to common molds are more an annoyance than a serious health threat. “Most molds, even if you can smell them, are not harmful,” says the UC Berkeley Wellness Letter. People who usually have an adverse reaction include those with lung disorders, such as asthma; individuals with allergies, chemical sensitivities, or a weakened immune system; and farmworkers who may be exposed to massive amounts of mold. Infants and the elderly may also be more susceptible to the effects of exposure to mold.

According to the California Department of Health Services in the United States, mold can cause the following symptoms: ‘Respiratory problems, such as wheezing, difficulty breathing, and shortness of breath; nasal and sinus congestion; eye irritation (burning, watery, or reddened eyes); dry, hacking cough; nose or throat irritation; skin rashes or irritation.’

Mold and Buildings

In some lands it is common to hear of schools being closed or people having to vacate homes or offices for mold remediation. Early in 2002, the newly opened Museum of Modern Arts in Stockholm, Sweden, had to be closed because of mold. Remediation cost approximately five million dollars! Why has this problem become more common recently?

The answer involves two main factors: building materials and designs. In recent decades construction materials have included products that are more susceptible to mold. An example is drywall, or gypsum board, which is often made of several layers of paper bonded to a hardened plaster core. The core holds moisture. So if this material remains wet for extended periods, mold spores can germinate and grow, feeding on the paper in the drywall.

Structural designs have also changed. Prior to the 1970’s, many buildings in the United States and in a number of other lands were less insulated and airtight than later designs. The changes resulted from a desire to make buildings more energy efficient by minimizing heat loss and gain and by reducing airflow. So now when water gets in, it tends to stay longer, encouraging the growth of mold. Is there a solution to this problem?

The most effective way of solving, or at least minimizing, mold problems is to keep everything inside clean and dry and to keep the humidity low. If moisture does accumulate somewhere, dry the area promptly and make the necessary changes or repairs so that water cannot build up again. For example, keep the roof and gutters clean and in good repair. And ensure that the ground slopes away from the building so that water will not accumulate around the foundation. If you have air-conditioning, keep the drip pans clean and the drain lines unobstructed.

“Moisture control is the key to mold control,” says one authority. Simple measures may spare you and your family from an encounter with the unfriendly face of mold. In some ways, mold is like fire. It can do harm, but it can also be extremely useful. Much depends on how we use and control it. Of course, we still have much to learn about mold. But knowledge of God’s amazing creations can only be to our advantage.

[Box/Picture on page 14, 15]


The Bible mentions “the plague of leprosy in a house,” meaning in the building itself. (Leviticus 14:34-48) It has been suggested that this phenomenon, also called “malignant leprosy,” was a form of mildew or mold, but about this there is uncertainty. Whatever the case, God’s Law instructed homeowners to remove infected stones, scrape out the entire inside of the house, and discard all the suspect matter outside the city in “an unclean place.” If the plague returned, the whole house was to be declared unclean, pulled down, and disposed of. Jehovah’s detailed instructions reflected his deep love for his people and for their physical welfare.

[Picture on page 13]

Medicines derived from mold have saved many lives

[Picture on page 15]

Drywall and vinyl can trap moisture, which then promotes the growth of mold