Are Mold & Mildew the Same?

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

Whether mold and mildew are the same thing or two different things is one of the most conflicted questions in the mold industry.

Many licensed mold professionals say mold and mildew are the same thing, while others say the opposite: that mold and mildew are two distinct phenomena.

And while those experts sometimes offer compelling data to back up their positions, more mold experts agree that mold and mildew are two different things, than agree that they are one and the same.

Mold and mildew are two different but closely related phenomena.

Many people use the terms mold and mildew interchangeably and while they do share some things in common, they are two distinct phenomena. Of the two, mold is far worse than mildew in terms of its ability to affect the health of a home and its occupants, as well as its ability to destroy things that it comes in contact with (grow on).

The Terms Mold and Mildew are Basically ‘Synonymous’

Ian Cull, the author of more than 50 courses on indoor air quality says that mold and mildew are, for all intents and purposes, virtually identical.

“For all practical purposes, think of the terms mold and mildew as being synonymous,” Cull writes in his 2017 book, “Fundamentals of Mold Remediation.”

He says also that some remediates or others use the words mold and mildew to describe fungi problems of varying intensities:

“Some make distinctions based on the following:

  • “Severity — small problems are mildew, big problems are mold.
  • “Substrate — growth in bathrooms is mildew, growth elsewhere is mold.
  • “Staining — mold is the organism, mildew is the staining it causes

But again, after listing those distinctions used by some, Cull says to think of the terms mold and mildew as being, basically, two words for the same thing (“synonymous”).

Official Definitions, Mold v Mildew

Since the topic is so conflicted, here are the definitions of mold and mildew according to official government bodies:

  • “Mildew (mold in early stage)….” — U.S. Federal Emergency Management Agency (FEMA)
  • “Mildew refers to certain kinds of mold or fungus.” — U.S. Environmental Protection Agency (EPA)
  • “The term mildew is often used generically to refer to mold growth, usually with a flat growth habit.” — U.S. Environmental Protection Agency (EPA)


Mold consists of organisms that have life but are neither plant nor animal.

Both living and dead mold spores can be dangerous and should be treated with great care and caution. Living mold spores are often referred to as “viable,” and dead mold spores are often referred to as “non viable.”

All living things are part of one of five distinct kingdoms, which we will define here specifically in contrast to mold.

  • Animal: Multi-celled, sexually reproductive, able to move on their own. Fish, birds, insects, etc.
  • Plant: Immobile, cells of cellulose, oxygen-releasing. Trees, bushes, crops, etc.
  • Fungi: Yeasts, molds, mushrooms, toadstools. Feed off of other living things, and they reproduce through spores.
  • Protista: Organisms not deemed animal or plant, such as algae, and protozoa.
  • Monera: Microscopic living things made single-cell organisms with no defined nucleus; bacteria.

Mold spores are part of the fungi kingdom. They get their nutrients from digesting organic material, effectively destroying it. What mold lives on is eventually broken down and caused to decompose.

Mold and mildew both require water to survive, and thus if you remove the water and moisture from an area, a surface, a fabric, or other item, you can effectively control both mold and mildew.

Ultraviolet light from the sun kills both mildew and mold.

The materials that mold digests include dead plants, dead trees, dead animals, and more.


Mildew refers to certain kinds of mold and fungus.

Mildew can be either “powdery” or “downy.” Powdery mildew affects flowering plants, beginning as white or gray speckles, which turn dark brown or black as it grows. Downy mildew starts yellow and turns brown.

If the factors causing it are left unchecked—moisture, humidity, darkness—mildew may be the beginning of a mold colony.

Mildew is, technically, a type of mold that grows on a living plant, but it is also defined as “mold in early stage” (FEMA) or as “the beginning of a mold colony” (Dr. Neeta Ogden, spokesperson, Asthma and Allergy Foundation of America).

“Mildew (mold in early stage) and molds grow on wood products, ceiling tiles, cardboard, wallpaper, carpets, drywall, fabric, plants, foods, insulation, decaying leaves and other organic materials.”

Federal Emergency Management Agency (FEMA)

This definition of mildew as “mold in [an] early stage” by the U.S. Federal Emergency Management Agency (FEMA), is a highly contested point.

Most mold remediators and other mold experts (doctors, naturopaths) would likely agree that even if mold and mildew are the same thing, the truth is: 1) That most mildew is in fact not the beginning of a mold colony, and 2) That most mold growth does not ever begin as mildew.

And, while you do remediate a mold problem, you do not remediate mildew.


The following important similarities exist between mold and mildew:


  • Mold spores are everywhere, requiring only the right conditions for growth to begin becoming visible to the human eye.
  • Mildew, technically speaking, appears on plants, usually that are still alive.


  • Both mold and mildew are forms of fungus.
  • Both mold and mildew can be killed with fungicide, or relocated to an outdoor out-of-home environment where they no longer affect building occupants.


  • Both mold and mildew require moisture in order to survive.
  • If you remove the source of water and moisture (whether it be a leaky roof or pipe, or the condensation from a hot shower), neither mold or mildew will be able to grow.


  • Mold and mildew grow best in humid environments
  • Neither mold or mildew can survive at freezing temperatures.


  • Mold and mildew both spread through the dissemination of spores, which can travel on clothing, pets, packages, in vehicles, or alone in the air.
  • Attempting to prevent the travel of non-visible mold is futile (useless), but care should definitely be taken to limit the spread of mold after working on mold remediation. In most cases, this means wearing disposable coveralls and other protective gear (booties, gloves) that are disposed of after each use. Clothing worn during mold remediation can be washed.



The following important differences exist between mold and mildew:


  • The easiest way to tell mold and mildew apart is by how they look.
  • Mildew is usually white, gray, or yellow, and is fluffy or powdery.
  • Mold is usually dark green or black and its texture is slimy or fuzzy.


  • Mold can grow on both organic and inorganic material including paper, fabric, wood, and food.
  • Mildew is unable to grow on synthetic or inorganic material such as plastic and metal.

“Molds can thrive on any organic matter, including clothing, leather, paper, and the ceilings, walls and floors of homes with moisture management problems. Mildew often lives on shower walls, windowsills, and other places where moisture levels are high.”

United States Environmental Protection Agency (U.S. EPA)


  • Mold has a higher vertical profile and projects itself off of the surface it lives on, even if ever so slightly.
  • Mildew is typically flat, or even with the surface it exists on.
  • Unlike mold, there’s not much mass to mildew.
  • (As a visual or mental comparison only, you can think of mildew as being like a very thin layer of flour on a kitchen table or cutting board, versus mold which would be similar to maybe a much larger amount of flour that’s been mixed with water.)
  • See what mold looks like here.

“Mildew refers to certain kinds of mold or fungus. The term mildew is often used generically to refer to mold growth, usually with a flat growth habit.”

U.S. EPA, “What is the difference between Mold and Mildew?


  • Mold is typically darker, whether a deep green, dark yellow-brown, or black.
  • Mildew can start off white or light yellow, then turn gray, brown, or black.


  • Mildew is unlikely to significantly damage the surface it rests on.
  • Mold creates long lasting and significant damage to structures. 

Ease of handling:

  • Mildew is more easily cleaned up and gotten rid of.
  • Mold removal may require the removal or repair of the surfaces it damaged.