What is Mildew, Really? The Difference Between Mold and Mildew

by | Jun 18, 2020 | Mildew, Mold | 0 comments

There’s a lot of misinformation and confusion out there about the difference between mold and mildew. Both are common types of household fungi and thrive in damp, humid environments. Because they share a number of key characteristics, it’s common for people to mistake one for the other or assume they’re equivalent.


In reality, mold and mildew are not the same thing (although mildew is a subclass of mold). Understanding the differences between the two is the first step in accurately identifying and effectively eradicating either (or both) from your home.


Mildew refers to specific types of early-stage molds that have a flat growth habit, rather than expanding outward like most other molds. Although they share many similarities, mold and mildew differ in appearance, growth patterns, and risks to human health.

What is Mold?

woman stressed because she found mold in her home

Mold is a broad term that refers to a variety of species of microscopic, filamentous fungi that form and spread on damp or deteriorating organic matter. There are more than 100,000 known species of mold, only some of which are prone to growing indoors. If left to grow without intervention, mold can cause damage to your home and pose a risk to your health.

What Does Mold Look Like?

Mold growth can appear in a variety of different colors and textures, generally forming in irregular patches. When trying to identify mold in your home and differentiate it from mildew, look for characteristics like:

  • A fuzzy, raised texture
  • Darker colors (which may appear gray, black, green, purple, yellow, or red)
  • A splotchy, dirt-like appearance

What Does Mold Smell Like?

Mold often carries a very distinctive and pungent smell. It’s most commonly described as smelling “musty” or “earthy,” although some people think it smells more like rotting food or meat. Many homeowners smell mold before they see it.

How Does Mold Form?

Molds begin to form in new locations by reproducing and then releasing tiny spores that float through the air and land on a suitable surface. While mildew grows on top of flat surfaces, mold penetrates into the surface on which it’s growing, transforming it into a porous material and breaking it down, causing lasting damage.

Excess moisture is typically responsible for indoor mold growth. Mold can form and spread on just about any organic matter where moisture and oxygen are present, including wood, carpets, paper, furniture, plants, and insulation material. 

Related: How to Get Rid of Mold in Your Home

Household mold is commonly found in bathrooms, basements, kitchens, and crawl spaces. It also often grows near leaks in roofs and windows or behind appliances where water has collected.


Health Effects of Exposure to Mold

woman sick in bed because of exposure to mold

Mold exposure can certainly impact human health. This impact may be minor or severe depending on a variety of factors, including the mold species, the length of exposure, and whether or not the individual is vulnerable. 

People who are at greater risk of experiencing severe symptoms of mold exposure include:

  • Infants and children
  • Pregnant people
  • Older adults
  • People with allergies or asthma
  • People with other pre-existing conditions or weakened immune systems

If you’re experiencing cold- or flu-like symptoms and you think mold may be the culprit, it’s important to get in touch with your doctor and contact a qualified mold remediation contractor.

What is Mildew?

mildew on a wall

Mildew is a specific type of mold; FEMA describes it as early-stage mold. Like other kinds of mold, mildew is a microscopic fungus that spreads by traveling through the air in the form of tiny spores. When these spores land in damp or humid environments, mildew begins to colonize and grow.

While mildew is unsightly and should be removed as soon as you notice it, it’s generally much easier to spot and get rid of than mold. Because mildew sits on top of the surfaces it grows on, all you generally need to remove it is a good household cleaner and a scrub brush.

What does mildew smell like?

One of the reasons mold and mildew can be so hard to tell apart is their similar odor. Both fungi produce a musty, earthy smell. If you notice this in your home, it’s likely that you have one or the other.

What does mildew look like?

Since mildew grows and spreads on top of surfaces rather than penetrating them like other molds, it’s often easier to spot in its early stages. Mildew is generally classified as either powdery or downy: 

  • Powdery mildew appears white or gray in color. Over time, it turns yellow and eventually dark brown or black. As the name suggests, it has a fine, powdery texture. 
  • Downy mildew appears initially in the form of yellow splotches. As it ages, these splotches typically turn a darkish brown.

How does mildew form?

Mildew forms and spreads in the same way as other types of mold, by reproducing and releasing spores into the air which eventually land and begin to grow. 

But unlike other molds, mildew doesn’t penetrate surfaces and grow into the materials it lands on (though it can still cause cosmetic damage). Instead, it grows on top of flat surfaces and often collects in places like the grout between your bathroom tiles.

Is mildew dangerous?

While mildew is not as dangerous to your health as certain types of toxic mold (including stachybotrys chartarum – commonly referred to as “black mold”), nor is it as damaging to your home, mildew should still be taken seriously. If you find mildew in your home,it’s important to remove it as quickly as possible in order to prevent adverse health effects and/or cosmetic damage.

Can mildew make you sick?

Like mold, mildew can cause health problems with prolonged exposure. While the fungi themselves are not toxic, certain species produce mycotoxins, which can cause mild-to-severe symptoms in humans. These symptoms are typically reminiscent of a cold or flu and are more dangerous if you suffer from a pre-existing condition like allergies or asthma.

The main reason mold poses a greater threat to human health is because it’s more likely to go undetected for extended periods of time. Because mildew is a surface fungus, it’s usually easier to spot and remove.

Related: 7 Ways to Deal with Mold Quickly to Avoid Allergies


How to Remove Mold vs Mildew?

person wearing yellow gloves cleaning off mildew

Removing mildew is generally much easier than mold. Because mildew sits on top of surfaces in your home, rather than penetrating them, it can typically be removed with a high-quality household cleaner and a good scrub brush.

Mold, on the other hand, can sometimes be difficult to remove. Proven DIY mold-removal methods include:

  • Chlorine-bleach solutions
  • Hydrogen peroxide
  • Distilled white vinegar
  • Rubbing alcohol

If you attempt to remove mold yourself, it’s important to take safety precautions. Wear protective gear such as gloves, glasses, and a face mask, and make sure you thoroughly wash or discard any items you used to remove the mold.

If you have a severe or recurring mold problem in your home, or if you’re particularly vulnerable to mold exposure, it’s best to hire a professional mold remediation company to handle mold removal on your behalf. 

difference between mold and mildew

Concerned About Mold and Mildew in or Around Your Home? Contact a Professional!

Minor mold and mildew issues can often be handled by the homeowner without the need for professional intervention. However, if you think you may have large amounts of mold or mildew growing in your home or are suffering from unexplained cold- or flu-like symptoms, expert testing is likely in order.

The state-of-the-art laboratory and team of expert consultants at JSE Labs are here to help. We offer accredited testing services and inspections and can help you determine the best course of action to keep you and your family safe.

Contact us online or give us a call at (503) 659-8338 today to get started!

Jennifer Malgren

Jennifer Malgren

Jennifer is the Laboratory Manager of JSE Labs, and holds a BS in Environmental Studies & Science from Portland State University. She is an avid learner and enjoys exploring new topics related to natural processes and the environment. She has experience analyzing hazardous materials, including asbestos and lead, and is committed to promoting safe and sustainable practices in the workplace and beyond. When not in the laboratory, Jennifer can be found exploring the Pacific Northwest with her Catahoula Leopard Dog, Oliver, or volunteering locally.

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