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What Causes Mold?

Indoor mold is not pleasant to talk about. But if you’re a homeowner, it needs to be discussed.

While mold is more common in some parts of the country than others, you need to fully understand this source of indoor air pollution no matter where you live.

Preventing a mold problem is important for all homeowners, and it starts by understanding the causes of this little fungus.  

mold damage

What is Mold?

Mold is a fungus that grows from microscopic spores (tiny particle sizes) that float in the air, slowly growing into colonies that can cover areas both large and small. While the mold itself can take many different forms, the mold is made up of hair-like structures that can only be seen at the microscopic level. To reproduce, a mold colony releases more spores that, given the right conditions, will eventually become new mold.

Mold is a living, breathing life form that needs all the basics of survival, including the right conditions, water, and food. While it is a natural life form, it can be harmful to humans, especially in high concentrations.

Dangers of Mold

Mold is not only unpleasant to think about, it’s also potentially dangerous to your health for many different reasons. If you are allergic to mold spores, you will obviously have issues when exposed to mold.

However, mold can also release various toxins that are dangerous to all people. Different molds will produce different toxins, creating a variety of risk factors for each mold species. These are sometimes referred to as black mold or toxic mold.

Some species of mold produce a substance called mycotoxins, a term that refers to any toxin produced by a fungus. Mycotoxins are considered some of the most dangerous substances in the natural world. Unlike mold spores, mycotoxins are not actually alive. They are, however, extremely small and cannot be seen by the human eye. Mycotoxins can be absorbed through the skin, eyes, or through breathing.

A condition called hypersensitivity pneumonitis or “HP,” is often caused by mold. This condition is marked by a hypersensitivity to inhaled organic substances, including mold spores. Mold can also be an irritant to people with chronic lung conditions, compromised immune systems, and serious infections in the lungs or bronchial tubes.

What Does Mold Need to Survive?

Now that we understand what mold is and why it’s harmful, we can take a look at what it needs to survive. With this knowledge, you can then make strategic efforts to maintain a mold-free house.

And as you’ll discover, the survival needs of mold are not much different from our own...

moisture inside window


The first thing that mold will need, just like the rest of us living species, is water. Mold is incredibly resourceful when it comes to staying hydrated; according to North Carolina’s Health and Human Services, mold can survive in a home with one of two sources of water: water intrusion, such as leaking pipes or seeping walls, and water vapor, which means high humidity and steam.

That’s right, water in the air is enough to keep mold alive.

In many cases, you will discover that rainwater or groundwater seeping into a basement is the cause of mold. Water can find its way into the home through leaky walls, windows, doors, or cracks in the foundation. Severe flooding is also a cause of mold, but this form of water damage is less common than small, less-noticeable leaks. Old foundations can also allow water to seep into a home, creating damp conditions that are just right for mold.

If mold can’t get solid water, high levels of moisture in the air can provide the resources it needs.

Mold has the ability to pull moisture directly from the air, making it an incredibly resourceful life form. To keep mold exposure down, indoor humidity levels should be kept below 60%, according to the EPA. They recommend, however, 30 to 50% for the best long-term results when it comes to reducing chances of mold and mildew.

Food (Nutrients)

Mold also needs a source of food and nutrients to survive.

According to the Florida Solar Energy Center, all mold really needs for food is anything that contains carbon atoms. Almost any organic substances will do, including wood, fruit, and even the oil from your skin.

installing drywall

In a house, building materials made from wood and paper are usually the favorite meal, providing enough nutrients to sustain large colonies of mold. In many cases, mold prevention starts by building a home with materials that do not provide nutrients, such as mold-resistant drywall.

A Comfortable Temperature

Finally, mold also needs a comfortable place to settle down, with the right temperature and the right conditions. Mold growth is highest in temperatures ranging from 70 to 90 degrees Fahrenheit, although it can survive in conditions from freezing to as high as 120 degrees.

It also prefers areas with stagnant, unmoving air, which is why energy-efficient homes, with little circulation, are more prone to mold growth. This also explains why damp basements may be more susceptible to mold growth.

If there is food, water, and the right conditions, there is a strong chance that mold could grow in your home.

Areas of the Home that are Susceptible to Mold

It’s possible to have mold in any area of the home, but the chances of mold growth are particularly high in three specific locations.

stairs to basement


Basements, especially damp basements, are often the top place for mold to grow in a home. Many basements have seepage and leaking problems, which provides water, while exposed wood and drywall can provide the organic nutrients mold needs to grow. Add in the fact that basements typically have low air ventilation and you have a perfect environment for mold to make a happy home.


The next place you might find mold is in the bathroom, largely because of the sink, toilet, shower, and other sources of water. Leaky plumbing can be a problem that causes mold, but it’s not uncommon for simple moisture left from a steamy shower, over time, to cause the growth of mold.

Sometimes the mold will hide in unseen areas, such as behind the toilet, underneath the sink, or even below vinyl flooring. A top defense in the bathroom is your ventilation fan, which helps remove moisture, dry the bathroom, and prevent mold growth. You can also use a mildew-resistant shower curtain, and wash and dry bathroom rugs frequently.


Kitchens are the next obvious place for mold.

Like bathrooms, they are often wet, meaning mold has the water it needs to thrive, but kitchens also provide a full banquet of nutrients, including food both inside and outside of the refrigerator.

If mold is growing in and around a kitchen, you’ll often find it in hard-to-spot locations, such as the area underneath a kitchen sink, or in the back of base cabinets.

To help prevent mold and mildew from becoming a major problem in your kitchen, be sure to check fruits and vegetables on a regular basis, and inspect dark areas around the sink about once a week.

Make sure all plumbing is sealed tight, and don’t let water stay on the floor or countertops for too long.

Can’t See Mold: Use Your Nose

Mold likes to hide in dark, damp corners of the house, in places where you likely won’t see it.

So, if you can’t see mold, how can you tell if it’s in your home?

You can use your nose!

First, we should mention that smell is not a replacement for visually scanning for mold. However, it can be an effective tool for detecting the problem in your home.

Beyond your eyes, your nose is probably the best tool for discovering mold. If your entire home or certain rooms have a constant musty odor, it could be a sign that mold is present in a hidden location.

If you run your heating or air conditioning system and notice a musty smell, you may have mold in your vents or ductwork. In this case, professional assistance and possibly mold remediation is likely needed.

Prevent Mold with Air Purifiers from Oransi

If you are ready to take a comprehensive approach to preventing mold, then you need to include an air purifier from Oransi.

Specifically, you need the best air purifiers for mold, such as the Mod+ Air Purifier, which uses MERV17 air filtration to capture airborne mold spores, reducing the chance of reproduction.

Contact us for more information on air purifiers and mold prevention. We’ll help you make an informed decision on allergen, dust, and pet dander removal.

From large purifiers for commercial locations, to small, quiet purifiers that fit perfectly in a child’s bedroom, we have world-class products that go above and beyond the highest industry standards.

If you are looking to improve the ventilation in your home and reduce your air conditioning costs, check into a whole house fan. These systems can complement your air conditioner while also providing much needed ventilation to improve your indoor air quality.