Is It Mold or Mildew? Learn To Spot the Difference

Right from the start, it’s important to realize that mold and mildew aren’t two different things. Mold and air quality expert Michael Rubino puts this fact in no uncertain terms: “Mildew is just a variety of mold. It’s not a separate entity.”

So why does this group of pathogens that you find growing both inside and outside the house have two separate names? Well, it’s a bit like freshly brewed vs. instant coffee. They’re both types of coffee, but any discerning individual who enjoys a daily cup would never mistake one for the other. I like to think of instant coffee as “coffee lite:” It’s easy to make and tastes like coffee, but it has none of the depth and fragrance of the freshly brewed variety.

In the same vein, mildew is a bit like “mold lite.” It lacks the toxicity of actual mold, it doesn’t have deep roots, and it’s easier to clean up. It’s an irritant, though, and like mold, it isn’t something you want to have around the house. “Both need to be prevented from growing indoors to avoid negatively impacting the indoor air quality and causing unwanted exposure,” warns Rubino.

Here’s how to tell if you have a mold or mildew infestation and what to do about it.

Mold vs. Mildew: What Is It?

Mold and mildew are fungi. They reproduce by the dispersion of microscopic spores, and they establish colonies in places where there’s enough moisture and nutrients to support their growth.

It’s not like you can keep spores out of your house. According to the United Water Restoration Group, the normal spore count in a typical room is from 200 to 500, and even a count as high as 1,500 is considered normal. Thousands of different mold and mildew species exist, and the characteristics of a colony depend on which species has found conditions suitable to establish itself.

How To Identify Mold vs. Mildew

Mildew — or mold lite — is more of a surface growth than other molds, which have roots that can penetrate deeply into the substrate on which it’s growing. Here’s how to tell the differences between them.

Mold vs. mildew: What does it look like?

Mildew generally has the following appearance:

• Powdery;
• flattish;
• generally white or gray;
• grows on surfaces and is relatively easy to brush or wipe off.

More serious molds, on the other hand, display these characteristics:

• Raised texture, with some species appearing fuzzy or slimy;
• varied colors, with the most common being green, gray, brown and black;
• has deep roots that make it more difficult to remove than by simply brushing or wiping.

Mold vs. Mildew: How does it smell?

Both mold and mildew smell musty, and the difference between their odors is largely one of degree. Compared to mildew, which smells mildly earthy and may be slightly irritating, other molds have a stronger, more pungent odor. Think of the smell of damp towels (mildew) vs. rotting wood or vegetation.

Mold vs. Mildew: How to test for it

You can often tell the difference between a mold and mildew colony simply by trying to brush it off. If you’re successful, it’s probably mildew and, if not, it’s more likely to be another type of mold.

If you want to know which species of mold it is and whether it’s toxic, you can use a home test kit and send a sample to a lab to identify it, but it’s more efficient to call in a pro. However, it doesn’t matter which species it is because, as far as the EPA and CDC are concerned, you should avoid breathing spores from any species, and you use the same procedure to clean all of them.

Other tips for identification

Another way to distinguish between mold and mildew is the substrate on which you find them growing. Because it’s a surface growth, you usually find mildew growing on non-porous surfaces, like bathroom tiles. Mildew is also more common than mold in dark places with limited moisture, such as attics, drawers and closets.

Mold, on the other hand, is more common in damp places, like basements and laundry rooms. Because its roots penetrate porous surfaces, it often grows inside materials like drywall, old wood, the grout surrounding bathroom tiles and behind old caulk in the shower or bathtub.

Mold vs. Mildew Prevention

“The key to preventing mold and mildew is to reduce moisture and the number of particles like mold spores in a home,” says Rubino.

How to prevent mold

Mold is more heavily dependent on moisture than mildew. Here are some methods Rubino recommends for reducing moisture:

• Clean up spills and pooled water ASAP;
• Hang up wet items, such as bathmats, towels and wet clothes, to dry;
• Separate the shower curtain and liner so that they can dry;
• Allow appliances to dry out after use (ex: leaving the dishwasher door open after unloading);
• Fix leaks;
• Crack the bathroom door and turn on the exhaust fan or open a window while showering to create airflow

How to prevent mildew

To prevent mildew, you also have to control moisture, but it’s just as important to reduce the spore count in your living space and remove spores before they have a chance to grow. Here are some ways to do this:

• Deep clean regularly;
• Dust often;
• Invest in air purifiers, particularly a whole-home purifier;
• Maintain the HVAC system;
• Upgrade the highest grade MERV filters the HVAC unit can handle and change them on time;
• Invest in a HEPA vacuum cleaner;
• Maintain an indoor humidity level of 35 to 50 percent.

Mold vs. Mildew Removal

“Successful remediation,” says Rubino, “involves identifying and eliminating the source (of moisture) that allowed mold to grow, removing the active infestation, and addressing all related contamination.”

How to remove mold

On non-porous surfaces, Rubino recommends applying a botanical cleaner, letting it sit for 30 seconds, wiping thoroughly with a microfiber cloth, and repeating twice more. Because mold has roots, removal from porous and semi-porous surfaces is more challenging. “The process is similar to pulling a weed—roots and all,” he says.

First, don’t use bleach, as it doesn’t penetrate porous surfaces and kill roots. Scrubbing with a good cleaning product is your best option. Rubino recommends applying hydrogen peroxide to semi-porous surfaces like tile grout to lift the spores to the surface and make them easier to wipe away.

Professional cleaner Michael Bogoyavlenskiy suggests a similar procedure for removing mold from tub and tile caulk. He says to mix hydrogen peroxide with bicarbonate of soda to make a paste, leave it on the caulk for several hours, and then wipe it away.

How to remove mildew

Because it doesn’t take root to the same extent as other mold, mildew is much easier to remove than mold. You can often simply wipe it away, and when you can’t get all of it that way, just scrub with the same cleaning agent you would use to clean mold from a non-porous surface.

Mildew sometimes grows in fabrics and upholstery. You can remove it by washing fabrics in the washing machine or using a HEPA vacuum cleaner to suck it off upholstery.

About the Experts

• Michael Rubino is a mold and air quality expert, environmental wellness advocate, and founder of HomeCleanse, a revolutionary company with the vision to end the worldwide health epidemic caused by poor air quality and toxic indoor environments.
• Michael Bogoyavlenskiy is the CEO of Cleaning Express, a domestic cleaning company and a professional facilities’ management provider servicing luxury offices, business centers, retail companies and other establishments.

Sources

• United Water Restoration Group: Mold Species & Mold Spore Levels; (2024).