What are the Causes of Mold?

Mold needs six elements to grow. A deficiency in any condition will result in mold cultures not being able to take hold or flourish. It will also cause a mold colony to die if one or more elements are removed after mold colonization has been established.

Reducing or removing these elements is the core strategy for preventing mold. It’s also the attack for destroying an existing mold colony. Here are six factors that cause and contribute to mold growth.

  • Mold Spores
  • Moisture
  • Food Source
  • Oxygen Supply
  • Lack of Sunlight
  • Optimal Temperature

Mold Spores

The first element is the mold spores themselves. This is hard to prevent, as mold microorganisms are almost universally present throughout the world. Spores are invisible to your naked eye and usually enter your house from the outdoors. The air movement of spores is the most common method for spreading them, followed by being introduced through contaminated materials.

Removing mold spores from your home is practically impossible. Keeping conditions, especially moisture under control, is the best option you have. The only places on earth that mold cannot occur is in the deserts and the ice lands since they’re far too dry and cold. Mold also doesn’t happen in lakes or under the ocean because of the lack of oxygen.

However, where the next five elements occur, you can be sure mold spores are there as well, just waiting for optimum conditions to form and grow.

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Moisture (the only controllable factor)

Without moisture, mold cannot possibly live. Water is the key to all life, and mold is no exception. There is no specific moisture content or humidity threshold where mold can’t survive. It depends on a blend of all the elements. Where it’s highly humid or even slightly damp, you can be sure there’s a potential for mold.

The longer wet or moist conditions exist, the more chance there is for mold to begin to grow. Most of the mold in homes start in hidden places. The common cause of dampness is a minor plumbing leak under a bathroom or kitchen sink that goes unnoticed or unattended for even a short amount of time.

Mold also starts in places you can’t even see, such as in ceilings where moisture intrusion from a roof leak isn’t caught and repaired. Mold also takes foot inside walls due to water lines, and drain-waste and ventilation plumbing pipes that have cracked or separated. Dampness can also happen from condensation where plumbing lines are chilled, and a high-humidity environment causes condensation.

It doesn’t have to be standing water that gives enough moisture to allow mold to grow. Bathrooms are notorious for containing active mold growth. Around toilets, and the corners of showers that never completely dry are common places you’ll see small, black patches forming on grout lines. Shower curtains and door tracks are other locations where mold can easily begin.

Moisture is the primary element necessary for mold to exist. If you remove sources of moisture, you can win your fight against mold.

Visible Moisture

roof sheathing in attic showing moisture intrusion during mold inspection

Moisture Meter

moisture meter testing wood for moisture content and potential mold

Lab Tested

mold inspection samples under a microscope

Food Source

Because mold is living, it needs food to survive and reproduce. Food sources outdoors are endless, where vegetation and other organic materials are found. In wooded areas, you can find mold everywhere from under old logs to the trunks of trees, as well as in the soil and grass. Mold is even present on rocks.

Your house is a different story. It’s also full of food for mold that you wouldn't think of. When you find mold in your bathroom or a closet corner, it’s feeding off the organic materials contained in wood panels or on wall materials. It’s also feeding on minuscule amounts of dust and dirt that are there no matter how well you clean.

Mold takes hold of all kinds of things around your home. It can feed on the insulation in your attic and walls, and it can feed on the back of the drywall. Mold even feeds on the surface of clothes and luggage. It consumes residue left on smooth tile surfaces and microscopic materials trapped inside porous flooring like carpets. And it loves damp cardboard, newspapers, and fabrics.

Mold also gets food from the air we breathe. Mold spores aren’t the only thing that’s microscopically present in the air that circulates your home and that you inhale all day. There are countless airborne particles mold can feed on, such as dust and pollens. Air even contains the spores of other mold species that contribute to their diet.

Removing food sources for mold is impossible, so it’s a waste of time to try. The trick is controlling the other elements, especially moisture, which is the only controllable element in eliminating mold.

Oxygen Supply

Mold can’t live without oxygen, as it needs air to grow and reproduce. Without oxygen, mold can’t perform the organic process dividing cells and forming mold mass. That includes making a steady production of spores that it depends on to spread.

Air doesn’t just contribute to mold’s physical, chemical, and biological growth. It is the principal carrier for mold spores so they can move to different locations. The spread may be an inch or two within a tight corner, or it may well be between rooms or across the entire house.

Be aware that it doesn’t take large amounts of air to help mold move and grow. Air is still present inside wall cavities and within the insulation. Sealed boxes and closed containers still have ambient air, and it’s there to help mold colonies grow. Trapped air still holds oxygen, and it doesn’t take much to allow mold to form.

As is with food sources, it’s virtually impossible to remove air in places where mold will grow. In fact, one of the best weapons in the war against mold is lots of air. Meaning, moving air through proper ventilation allows damp or wet surfaces to dry through evaporation and to keep mold growth at bay.

It all comes back to controlling moisture, as moisture is mold’s best friend in ensuring survival, along with a limited amount of sunlight.

Lack of Sunlight

Exposure to direct sunlight is deadly to mold. The ultraviolet rays in natural sunlight destroy mold’s cellular structure, and this is why you’ll find mold outside in dim and dark places such as under a forest’s canopy or on north-facing rock and tree trunks.

Indoor lighting doesn’t have the same crushing effect on mold. The light spectrum of artificial lighting is different from sunlight and doesn’t give off the same type of photons that kill mold and stop its growth. While mold prefers limited light or even total darkness, it still grows inside homes where incandescent or fluorescent lights are visible.

It’s not possible to soak your entire house in sunlight, but there are types of indoor lighting on the market that emulate the sun’s wavelengths and can destroy mold through its exposure, but unfortunately, this isn’t practical or economical. Mold is going to take hold in those dim places where light is limited, but warm and wet conditions are found, but having the right temperature makes a difference in mold growth as well.

What Other Inspectors See

drywall ceiling with water stain showing moisture intrusion

What We See

infrared image showing moisture intrusion on the ceiling

Optimal Temperature

Mold can’t tolerate conditions that are too cold or too hot. You won’t find mold occurring in arctic regions, and you won’t find it in the desert. Freezing will destroy mold or at least make it dormant. Burning it also destructs mold’s cellular structure, which prevents it from growing and spreading.

Temperature levels inside most homes and businesses are at optimum levels for mold cultures to live. Temperatures between 72 and 81 degrees are perfect for mold to grow, especially in the damp and dark areas. Mold spores cannot take hold or grow near the freezing point but can survive well above temperatures that are uncomfortable for humans.

Relative humidity levels are also an important factor in allowing mold conditions to get out of control. High humidity gives the wet, moist environment that mold loves. The EPA recommends you keep your home between 30% and 50% relative humidity, with a maximum being 60%. Any humidity levels above that will exponentially allow mold growth.

Regulating the temperature in your home to fight mold doesn’t work. Although the optimum temperature is one of the six-elements that lets mold exist, it’s a minor player compared to moisture.

If you control moisture in your home, you’re well on your way to preventing mold from taking hold and growing. But that’s easier said than done, as moisture that gives mold its head start, it can be hard to spot.

Let the IAC2 certified experts at Raleigh Mold Inspection perform and inspection according to the IAC2 standards of practice to help you take the next steps in combating mold in your home.

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