Mildew vs. Mold: What's the Difference?

By: Patty Rasmussen  | 
mildew on books
Portugal's National Archives is in possession of these beautiful books. Unfortunately, mildew covers these books, which are only from the 1950s. Catarina Carvalho/Unsplash

Many people use the words "mold" and "mildew" interchangeably, but they are not the same thing. So, no, you can't bail on your neighbor's Jell-O party with the excuse that you have to deal with a bad case of mildew/mold in your crawl spaces.

Both are scientifically classified as fungi (spore-producing organisms) and can emit a musty smell. And there are some similarities between the two other than their scientific classification, but they are each distinct.


Mold and mildew spores are everywhere. By the time you see mold or mildew, you're looking at a colony of millions of tiny spores. Read on to learn how to identify and treat mildew vs. mold.

What Is Mildew?

Mildew refers to mold in its early stage and is typically fast-growing. The spores are either water-, air- or insect-borne. Both mold and mildew like porous, organic material on which to grow: wood, paper, food, insulation, carpet or clothing — all the things in a normal home.

The biggest difference between mold and mildew is on the surface. That's a little play on words because mildew grows on the surface of materials like your shower walls, windowsills and other places where moisture tends to be high.


Mold, however, consists of microscopic fungi that penetrate the surface of whatever it's attached to and grow below.

So the powdery, fluffy spores you see on books and boxes in your basement? That's mildew. But good news! It's only on the surface.

How to Prevent Mildew Growth

If you find mildew, you can clean it off so the spores can't multiply or damage anything it's on. Then check the room's ventilation and maybe add a dehumidifier to the space. Bathrooms should have an exhaust fan to vent out warm, moist air. Check the seals around windows to prevent condensation.


What Is Mold?

molded house
Mold starts to grow within 24 hours of a home or structure flooded by water, and it can hide inside interior walls, causing structural damage. D_Townsend/Shutterstock

Mold is a different matter. It can be fuzzy or slimy. Mold growth happens on the surface of organic material and then penetrates it. Mold is usually white, blue, green, brown, gray or black.

Mold is only a problem when it grows indoors. Over time, mold will rot the organic matter that it covers. That's why mold often causes structural damage to homes and belongings, leading to mold remediation strategies and costly repairs.


Mold also can have serious health effects. It produces allergens that can trigger severe allergic reactions, including hay fever-type symptoms — sneezing, runny nose, red eyes and skin rash.

Mold can prompt severe reactions, like asthma attacks, in people who are allergic to it. Mold exposure also might cause irritation to eyes, nose, throat and lungs to people who aren't even allergic.

Doctors and scientists continue to research the effects of mold inhalation; in 2012, the National Institute for Occupational Safety and Health (NIOSH) published guidelines stating "Studies have shown that exposures to building dampness and mold have been associated with respiratory symptoms, asthma, hypersensitivity pneumonitis, rhinosinusitis, bronchitis and respiratory infections." In 2019, NIOSH released updated guidance on how to best assess dampness in structures to prevent health problems.

This type of exposure to mold would likely occur during the cleanup of a home or building after a flood. The U.S. Centers of Disease Control and Prevention (CDC) says mold will start to grow within 24 to 48 hours in a flooded structure if it's not properly dried.

Mold Removal and Prevention

Unlike mildew, which you can easily clean yourself, the CDC says removing mold is very difficult; a qualified mold remediation professional certified by the National Environmental Health Association (NEHA) or the American Industrial Hygiene Association (AIHA) can remove and clean mold.

But there are a few things you can do to prevent mold. According to the CDC, you should:

  • Keep humidity levels low in your home.
  • Use mold-killing household cleaners in your bathroom
  • Turn on exhaust fans
  • Fix leaks.

In short, you want to avoid having damp areas and unchecked moisture levels in your home.


Similarities and Differences Between Mold and Mildew

They are both filamentous fungi — multicellular fungi with branching tubular structures (hyphae) that form a mass of intertwining strands. They crave especially damp, moist environments and both can grow on things in your home.

But mildew is usually easier to get rid of. And that goes to the heart of the differences between the mold and mildew.