Mold vs. Mildew: What’s the Difference?

Mold and mildew are two types of fungi that no homeowner wants to discover indoors. These microorganisms can spread easily, affecting large areas of your property with visual and structural damage while creating potentially serious health problems.

Both mold and mildew begin as tiny spores (seeds) that require a similar set of criteria to take a foothold and flourish, making them easy to confuse. However, the two have striking differences in appearance, health effects, and seriousness that are important to understand to treat and prevent their occurrence in your home.

Differences between mold and mildew

Mildew and mold are both fungi, but mildew is not as invasive or troublesome. Mildew is a surface fungus that can be easily treated with a store-bought cleaner or bleach and a scrubbing brush. Mold is often a part of a larger infestation that may require professional treatment. Rather than growing on the surface of its host, mold penetrates the object it lives on and eats away at its cellular integrity.

These fungi also differ in appearance and potential health risks. Mildew is typically a gray, white, or light brown color and rests on the surface of a moist area. It has a powdery appearance and may be accompanied by a foul odor. Mold is usually black or green and has a fuzzy appearance and a distinctly musty smell.

While mildew can cause minor respiratory problems like coughing fits, it poses less of a threat than mold. A significant mold infestation can cause a host of issues that range in seriousness based on the health of the individual it comes into contact with.

According to the CDC, persons in good health may experience sneezing, dry skin, nasal stuffiness, and itchy throat, whereas those with severe mold allergies, asthma, chronic lung illnesses, and other serious health issues may experience chest tightness, shortness of breath, and lung infections.

Common types of mold and mildew

Mildew is thin, superficial, and flat in appearance. It can thrive on many damp surfaces including clothing, paper, leather, walls, ceilings, and floors. These are the most common types of mildew found indoors:

• Basidiospores—This variety is associated with dry rotted wood. These mildew spores eventually become mushrooms and can cause severe allergic reactions.
• Aureobasidium—Generally described as “bathroom mold,” this mildew is found in showers and bathtubs.
• Botrytis—Often found in humid greenhouses, this type of mildew is found on indoor plants and can trigger asthma symptoms.
• Rhizopus—Dangerous to those with existing health conditions or nutritional deficiencies, this toxic mildew grows on garbage, house dirt, and food.

Mold is dark, sometimes described as hairy, and can grow into surfaces. These are the most common types of mold found indoors:

• Aspergillus—This is an allergenic mold with more than 185 species that’s often found on walls where it forms thick layers.
• Penicillium—This allergenic mold has a velvety texture and is bluish-green in color. Areas with water damage, mattresses, and wallpaper are its most popular host sites.
• Stachybotrys—Otherwise known as toxic black mold, this variety is slimy in texture, black or dark green, and found in damp areas left too humid for weeks or months at a time.
• Aureobasidium—This type appears pink, brown, or black, darkens as it ages, and is found on wooden surfaces.
• Cladosporium—Commonly found in carpets, this allergenic mold is olive green and suede-like.

What causes mold and mildew?

Both mold and mildew need porous, organic material to grow such as wood, insulation, carpet, food, upholstery, clothing, or paper. They thrive in humid conditions where a light source is either poor or non-existent, and their growth occurs when their spores make their way into an area that’s suitable for colonies.

These spores exist relatively harmlessly in just about every breath we take, but the drama begins indoors when they encounter the trifecta of moisture, heat, and darkness, which encourages the spores to attach and multiply.

Where do mold and mildew form?

Mold and mildew have preferences with regard to where they like to take up residence. Mold is the most common type of fungus found on food; you can probably recall a time when, to your dismay, you discovered it on bread, meat, or cheese. Basements are also highly prone to mold after an event like flooding, but it can grow under “normal” conditions, too.

This fungus isn’t picky and will take root just about anywhere that oxygen, warmth, darkness, and moisture come together. Common growth spots include fireplaces and chimneys, walls, furniture, insulation, mattresses, and crawl spaces.

Mildew, on the other hand, is a thin, surface fungus that doesn’t penetrate its host. It’s most commonly found on floors, walls, ceilings, and areas with humidity, like bathrooms, kitchens, and basements. It’s common to see mildew in the corners of a shower or in a bathtub, but it can also be found on porous items that are left wet for too long like fabric, paper, and leather.

Effects of mold and mildew

Mold and mildew spores typically can’t be seen by the naked eye until they’ve multiplied into a colony with millions of spores. In small colonies, neither mildew nor mold is a serious problem when taken care of quickly. Mildew is the least threatening of the two because it grows only on surfaces and can be easily remedied with household cleaner, but it can cause minor respiratory issues if left untreated.

Mold is a completely different story. Not only is it slimy and unsightly, it can cause serious structural damage. As a predecessor to wood rot, moldy hardwood floors can warp and buckle. When trapped underneath flooring, mold can escape into the house and ruin furniture, carpets, and other areas once the foundation is exposed. 

Homes with serious infestations may require the replacement of walls or entire roofs. Mold growing in the basement often goes unnoticed for months or years and can spread up into other rooms.

Not to mention, toxic black mold can cause serious reactions upon mold exposure. This type secretes chemicals known as mycotoxins, which wage gorilla warfare against your body, slowly entering through your skin, nose, and mouth, and lodging in your lungs, stomach, and other areas. In extreme cases, it can cause memory loss, hearing damage, and cognitive failure.

Signs of mold and mildew in your home

Mildew can typically be detected via sight. You’ll know mildew by its powdery appearance and white or gray color. Mold can be more difficult to detect because it grows on food and more permanent structures, including the interior of those structures.

If you’re unsure whether you’re looking at mold or mildew, an easy way to distinguish between the two is to place a few drops of bleach on the affected area. After five minutes, check the spot for any differences. If the area is lighter, you’re likely dealing with mildew, but if the spot is still dark in color, it’s probably mold.

Another way to determine the presence of mold is to purchase an at-home test kit. These kits are sold in stores or online and use petri dishes to capture mold scores. After the petri dish has been exposed to the home’s air for several days, it’s returned to the manufacturer, who reports back to you whether mold is present. While these kits are helpful for preliminary screening, they won’t help you locate the mold’s source.

Professionals have more advanced methods of testing, including air sampling, surface testing, and bulk testing. Air sampling tests the concentration of spores in the air. In surface testing, samples are gathered through swabbing or tape lifting and then examined in a laboratory.

Bulk testing is the most thorough of the three methods and involves collecting materials from throughout your home and inspecting them in a lab for mold. The benefit of bulk testing is that you’ll be able to pinpoint the areas with the highest concentrations.

How to remediate mold and mildew

If you’re dealing with mildew, the remediation process is simple.

How to remove mildew

1. Using rubber gloves, treat the area with bleach or a household cleaner.
2. After, scrub with a disposable toothbrush or rag until the mildew is gone.
3. Mildew on clothing can be removed by using a toothbrush and a cleaning solution to scrub the infected area and then washing the item by itself in hot water.

How to remove mold

With mold comes the question of whether to go at it alone or hire a professional. If you find mold in your home in small concentrations on easy-to-clean surfaces like windows, tubs, tiles, and sinks, it will usually succumb to a bleach and water solution.

Hiring a mold remediation specialist

According to the EPA, if you find mold spores growing on studs, subflooring, your HVAC system, or drywall in an area that exceeds nine square feet, it’s best to hire a professional mold removal service. Improperly treating serious infestations can cause cross-contamination to other areas.

Factors to consider

• When hiring someone to clean mold, check references and ask about their approach. You want to make sure they’re as thorough as possible.
• The mold remediation cost will vary by where you live and the seriousness of the infestation, but you can expect to pay between $500 and $4,000.
• The time it takes to remediate mold will depend on how much mold is present, where it’s growing in your home, and the type of material it’s growing on. Most mold remediation takes one to five days, but very serious cases of toxic mold can take weeks or months.

How to prevent mold and mildew

The primary way to prevent mold and mildew in your home is to eliminate moisture and maintain a good standard of housekeeping. As in any battle, it’s best to invest in prevention upfront instead of scrambling to remediate mold and mildew when they’re at your door, in your shower, or on your window.

• Keep bathrooms well-ventilated—Use an exhaust fan while showering to circulate air and remove moisture. Spread towels after use to encourage drying, wipe down showers and bathtubs at least once a week, and shore up any leaks.
• Use dehumidifiers, fans, and open windows—These can encourage moisture reduction in other rooms. Moisture meters can detect the presence of moisture in ceilings, floors, and walls.
• Keep an eye on your HVAC unit—If you have leaky air conditioning duct joints, especially in the attic, seal them with a mastic-type sealant.
• Regular cleaning—Clean windows often to prevent moisture, dust, and debris from collecting. You should also consider deep cleaning your entire home at least twice a year.
• Avoid bringing outdoor furniture indoors—Outdoor furniture brought inside is a hot spot for fungus, as is firewood.
• Keep mold off household plants—Moist soil and leaves are an ideal breeding ground for mold. Try adding Taheebo tea to the water you give your indoor plants, as this tree oil helps them withstand fungi.
• Beware of exterior issues—These include separating roof shingles, cracked or loose door and window frames, cracked chimney masonry, and deteriorating sundeck flashing, all inroads for mold. Clean gutters regularly and ensure downspouts carry water away from the foundation.