What is the Difference Between Mold and Mildew?

What is the Difference Between Mold and Mildew?

The words “mold,” “mildew,” and “fungus” are enough to strike fear into the heart of any homeowner. They bring to mind images of damp basements or slimy, neglected bathrooms.

But the truth is, it’s inevitable that some corners of your house may become host to at least a few of the thousands of species of fungus that cause mold and mildew. 

What is the difference between mold and mildew? The difference between mold and mildew lies in the stage of growth of the fungus. We often use “mildew” to describe flat-growing, white fungal growths, and it sometimes refers to the early stages of mold growth. We often use the term “mold” to describe growths that are larger, slimy in texture, and colored green, orange, or black. 

There is not much practical difference between mold and mildew. The terms are often used interchangeably by the general public to describe the same thing; common types of fungi often found in and around homes.

Continue reading to learn more about the differences between mold and mildew and how to deal with fungal growth in your home. 

Mold Versus Mildew

Common names such as mold and mildew are often used in very vague and interchangeable ways, which can make it difficult to pin a particular definition onto them.

This vagueness is certainly the case for the words “mold” and “mildew,” which both refer to fungus, usually around the home.

What Is Mold?

In general, mold is the term people use to refer to fungal growths inside the home.

More technically, molds are multicellular fungi species that grow in a structure of filaments (hyphae), as opposed to yeasts, which are single-celled fungi (source).

A single mold organism is microscopic and invisible to the naked eye, so that gray fuzz you find on the orange you left too long in the fruit bowl is actually a mycelium: a whole colony made up of many interconnected hyphae. 

Molds reproduce by producing many minuscule spores, which can be transported by the movement of air or water, or by clinging to clothing, hair, and other substances.

These spores are too tiny to see and may remain dormant for long periods until the conditions are right for growth.

There are thousands of known species of mold-producing fungus in the world around us.

Molds don’t photosynthesize but break down and absorb the substance they grow on, which means they play an essential role in preventing the build-up of organic matter such as fallen leaves or dead animals. 

This organic breakdown is vital for recycling nutrients in the ecosystem, but can also spoil food and even destroy structures in your home.

What Is Mildew?

Essentially, mildew is the same thing as a mold. Whereas mold is a scientific term that refers to a particular kind of fungus, mildew is a common word without a specific biological meaning. In fact, most people use mildew simply to refer to mold growth (source). 

Some people distinguish between mold and mildew by color, using the word mildew to refer to white or pale grey mold growth, as opposed to black, orange, red, or green mold. 

Sometimes mildew is used to mean the fuzzy growth that grows on spoiled fruit. For example, while “mold” is reserved for slime mold, slime mold is technically no longer classified as a fungus (source). 

Some people also use the word mildew to talk about mold growth in its early stages (source).

All this goes to show that common names can be misleading and have little to do with the organisms that they actually describe. 

Ultimately, all you need to know is, whether you call it mildew or mold, excessive fungus growth in your house is not desirable, and it’s best to take steps quickly to get it under control.

Mold And Mildew In The House

Given how common and how essential molds are in the ecosystems around us, it’s clear that human beings have lived alongside these many species of fungi throughout our history.

But in modern times, indoor mold has become a source of concern and even lawsuits. The reason for this is probably a combination of changes in the way we live and changes in the way we think (source).

Homebuilders construct homes to be far more airtight for energy efficiency, which reduces the circulation of air and might increase moisture, encouraging mold to grow. 

Common modern building materials such as engineered wood are excellent breeding grounds for mold when they are wet. 

We are also far more sensitive to environmental health concerns and have growing medical knowledge about how our built environments can affect our health.

This knowledge increases our concern regarding mold growth in our homes, even before we see it.

Where Does Mold And Mildew Grow?

Almost all molds require high levels of moisture to germinate and survive.

This need for moisture means they are most likely to grow in persistently damp parts of your house, such as around leaking pipes or window frames, in poorly-ventilated bathrooms, and in basements where there is rising damp (source).

Mold also requires an organic food source, which can be provided by paper (such as your drywall panels), wood (like window frames), skin cells, or grease and food remnants on your carpet or shower curtain. 

Most molds require some warmth to grow, which is why refrigerators can inhibit mold growth on food to some extent. With enough moisture and the right temperature, mold can start growing immediately and spread within hours or days.

How Do I Know I Have Mold In My House?

Fungus spores are in the air all around us, clinging to surfaces and carried on our hair, our pets’ hair, and our clothes, so you have at least some mold in your house. This mold is not a problem unless you get a large growth of mold. 

If you have a considerable growth of mold or mildew in your home, you will probably be able to see it or smell it (source).

Visible signs of fungal growth include large discolored spots on walls or ceilings, especially in areas that have been water damaged. 

Mold appears in a wide variety of colors, from white to green, black, and even red. But if you suspect you have a mold problem, also remember to check hidden spaces, including behind paneling and under carpets (source).

You can also detect mold by smell. I’m sure you’re familiar with the scent of mold, which many often describe as musty or earthy.

In extreme cases, the smell can be foul, like dirty old clothes. Don’t ignore a musty odor if you can’t find the source: it may be a sign that you have a mold problem.

Once you have observed the signs of mold growth, you may want to conduct tests such as air or surface sampling to confirm the growth of mold. Read more about air sampling here: Does an Air Quality Test Detect Mold?

Is Mold Or Mildew In The House Dangerous?

Most of the time, mold won’t cause more harm than unsightly stains and a bad smell.

Still, depending on the type of mold, where it’s growing, and the size of the infestation, mold can pose a danger to you in two ways: by structurally undermining your house and by impacting your health.

Damage by Mold and Mildew

Based on the definitions as we’ve discussed them, most individuals would not consider mildew to be a risk to the structural soundness of a house because of mildew’s description as an early or superficial mold. 

In the early stages, mold may not cause structural damage to your house, but it can cause serious cosmetic damage to walls, ceilings, and floors. Someone will usually have to replace stained surfaces, which is not a small expenditure.

But in more severe cases, mold can cause structural damage.

Because it decomposes and absorbs the organic materials on which it grows, mold gradually eats away at that material, which can disintegrate progressively wooden roof trusses, floorboards, and other structural elements of a building (source). 

If you do nothing to stop it, this can pose a risk to your safety.

Health Risks from Mold and Mildew.

Some forms of mold are the culprits behind ringworm, athlete’s foot, and other skin conditions in human beings. 

Other molds can infect open wounds or cause severe and even fatal lung infections. These infections include histoplasmosis, which is transferred by infected bat droppings, or blastomycosis, which grows in infected soil and bird droppings (source). 

These diseases are usually endemic to particular areas, but the spores from more common molds can be the source of widespread and hard-to-pin-down health problems. 

The World Health Organization has recognized that people living in moldy buildings are more likely to suffer from asthma, respiratory diseases, and allergies and that resolving the damp issue often alleviates these (source). 

In mild cases, mold might cause no more than an irritating, persistent wheeze. Still, people who suffer from mold allergies may experience severe discomfort and even illness such as pneumonia, caused by inflammation of the lungs (source). 

Both those with mold allergies and those without can experience discomfort and illness from living in houses with large mold infestations.

Some molds also secrete mycotoxins as they grow on a particular surface. When you inhale, eat — or sometimes even touch — these toxins, you absorb them into your bloodstream, and they can cause severe illness and even death.  

Historically, scientists have linked mycotoxins to the death of farm animals that ate contaminated grain. They even linked it to pets that ate pet food poisoned with mycotoxin (source).

How Can I Prevent Mold and Mildew Growth?

Image by Shad Gross via FreeImages

Given how common molds are, it is impossible to prevent them from entering your house. Molds are a natural and vital part of ecosystems and, most of the time, they do no harm.

The key is to prevent large growths of mold in your house. To do this, you will need to be attentive and proactive.

Go to the Source of the Problem

Molds need moisture to thrive, which means roof or plumbing leaks are prime sources of mold growth.

So if you notice a mold problem, don’t stop with replacing the ceiling boards or repainting the wall. Look for leaks and repair them to avoid the problem recurring.

Address the Problem

Mold colonies can grow on wet surfaces in just 24 to 48 hours. So if you notice a moldy smell or a discolored patch on your wall, or if you have a flood or stormwater leak, don’t wait for it to get worse before you act. 

Routine Maintenance Will Save You Time Later

Clean your house regularly to stop any mold colonies from taking hold. Perform a deep clean of dark, damp corners and use strong detergent.

Regular cleaning also provides you with an opportunity to inspect the less-used areas of your house where mold may be likely to lurk.

Improve Air Flow and Keep the House Dry

If condensation is forming inside your windows, or the walls in your bathroom run with moisture when you shower, your house probably doesn’t have adequate airflow. You might end up with a mold problem. 

Run the fan or open the doors and windows while you’re showering. You should regularly open doors and windows throughout your house to encourage the through-flow of air.

Avoid carpets, especially in damp areas like bathrooms. Consider using a dehumidifier in places that can’t be naturally ventilated (source).

How Do I Remove Mold and Mildew from My House?

You can address most mold growth with a strong detergent and some scrubbing.

If your mold colony is small and easy to reach — about three feet by three feet — you can probably handle it yourself, but severe infestations might require professional help. 

Minor Mold Growth

You can scrub away tiny patches of mold growth in the corners of your shower by using bleach and a scouring pad.

But if you’re working on a dinner-plate sized colony in a confined corner of your basement, you’re going to want to gear up a little more.

Gather your mold-fighting tools. You’ll need a strong detergent, a potent bleach, and a scrubbing brush or scouring pad. Other useful tools include a scraper to remove any thick mold or peeling paint and a fan to help dry the surface.

Make sure you have the right protective equipment. An N-95 respirator mask is a low-cost piece of protective equipment that will prevent you from breathing in any spores while you’re in close contact with the mold (source). 

It is also best to wear gloves and goggles to protect your skin and eyes from the strong detergent you will be using.

Start by scrubbing the area with detergent, then rinse well. Disinfect using bleach but do not rinse. Allow the bleach to dry on the surface. 

If there isn’t adequate airflow, set up a fan to help the surface dry thoroughly. You should carefully observe the area over the next few days to make sure the mold is not growing back (source).

Remember that the surface may remain stained even after the mold is gone, and you might need to repaint walls and ceilings. You will probably need to throw away soft surfaces such as carpets and upholstery if they become moldy.

Major Mold Growth

If you suspect a major mold problem in your home, it might be time to call in an expert. Reasons for calling an expert include:

  • Concerns that the mold has caused structural damage to the building
  • Concerns that the mold is causing health problems for the occupants
  • It stems from a faulty air conditioning system, sewer, or plumbing

If you do call in an expert, make sure that they have experience dealing with mold.

There are many online sources to help you make your decision, including resources from the US Environmental Protection Agency. Your state may also have published guidelines for you to consult.

You may want to ask for testing to confirm the type and extent of mold growth, but you should bear in mind that testing is an expensive and imperfect process (source).

Testing can only provide a snapshot of the growth in a small area of your house on a particular day, and you may prefer to spend the money on eliminating the mold and redecorating.

Final Thoughts

Many people distinguish mold and mildew but, when it comes down to it, they are essentially the same thing: fungus. 

Although fungi make up a common and crucial part of the natural world, when they run riot in your home, it spells bad news for your health and that of the building.

Mold can cause cosmetic and even structural damage to your house, and can also cause severe health problems for you as the inhabitant.

It’s essential to address a suspected mold problem immediately and take steps to avoid the mold growing back in the future.


I'm a Pharmacist and a passionate researcher into clean air and pure water for the home. I believe these 2 elements play a significant role in our health and overall wellbeing.

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