Mold on Windows – 15 Things You Need to Know
Do you have mold on your windows? How did the mold get there? Is mold dangerous? How do you get rid of it? We answer all your questions.
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Mold on Windows – WHERE DID THE MOLD COME FROM?
From the arctic to equator and all the places in between, mold lives literally everywhere. Molds and mildew are fungi, and grow from microscopic spores that are everywhere in the air. Molds are important for recycling organic matter (such as leaves). The recycling process they perform returns nutrients to the soil, and is important for plants to grow.
In order to grow, molds need four things: oxygen, moisture, a food source, and the right temperature range (ideal is between 77F – 86F). It is difficult to impossible to control the temperature and amount of oxygen in the unconditioned spaces in your home (attic, crawlspace, behind cabinets, etc.). So, let’s think about the things you can control when it comes to mold.
Food Sources
Molds grow inside of their food sources. They penetrate deeply into drywall, carpets, floors, cabinets, underneath kitchen and bathroom sinks, etc. Anything with carbohydrates in it could be considered a food source for molds.
Moisture
Moisture is the one thing you can reasonably control when it comes to mold. A dry home equals a home with much less mold and mildew growth. Keeping areas dry, especially areas that use water frequently (like bathrooms), is important to prevent mold growth.
How Fast Do Molds Grow?
Moisture behind baseboards and cabinets, wet carpet tack strips, in crawl spaces, basements, and other hard to reach areas are a ticking mold time bomb. Once enough moisture is present, molds can begin to grow in less than 48 hours! Even with fans going and mopping up the water, it may not be enough to prevent mold growth.
How do I know I have mold vs. mildew?

Mildew is flat and grows on the surface of things. Mildew in the window sill is caused by the excess moisture from the window.
Mold and mildew differ in the way they grow and what they look like. Mildew is always flat, and may begin white and then turn brown, gray or black.
Mildew is flat and grows on the surface of things. This window can easily be cleaned by the homeowner and the mildew removed. (However, the moisture from the window could be a continuing problem.)

Mold is usually fuzzy and raised, comes in many colors, and always grows inside its food source. All of the drywall will have to be removed not just cleaned. This is a professional job.
Mold is usually fuzzy and raised above the surface that it is growing on. Mold can be many different colors ranging from white, yellow, green, gray, to black. The biggest difference between mold and mildew is how they grow. Mildew only grows on the surface. Mold grows inside of it’s food source. Mold has to be removed completely not just cleaned.
How does mold grow on windows?
Have you looked at your windows lately? I mean, really looked? We usually look through them, not at them. Windows are a great place for dust to collect. If you’re a fan of our blog, you know what dust is…Mold Candy!
Mold loves to grow in the dust of your home. Dust is made up of the most gross things you can imagine including: dead skin cells, tiny bits of food, soil particles, bits of dead insects, pollen, microplastics, bacteria, mold spores, and more. Molds use the dead organic material of the dust to grow and reproduce in the presence of moisture.

Moisture Plus Dust Equals Mold!
Whether your windows are wood or aluminum, if there’s dust and moisture, mold can grow there. Most of the time, people notice mold growth in spring or fall when they open the windows. Dust and mold growth build up over time in window sills both inside and out. With wooden windows, you have double trouble since the mold can even grow inside the frame itself! Keeping windows clean and dry prevents mold growth.
DOES MOLD REALLY CAUSE HEALTH PROBLEMS?
In one word… Yes.
Mold is most often associated with allergies and asthma, but mold is much more menacing than people know. While all molds have the potential to cause irritation and allergy symptoms, molds can also cause much more dangerous health problems including: fungal poisoning from mycotoxins to mental health issues.
Mold hides in places no one ever thinks to look like under cabinets, in crawl spaces, attics, and behind furniture. People may spend weeks, months, and even years fighting illness, and never know what they are really fighting…mold. Many of our customers find us after a recommendation from their doctor, that they may in fact have a mold problem, and not just an illness.
BLACK MOLD – SOMETHING OF A MISNOMER

The thing is… dangerous and toxic mold is not just black, it can be many different colors. Toxic molds can appear to be green, yellow, brown, and black.
Before we go any further, let’s clear up the confusion about ‘black mold.’ When you read about ‘toxic black mold’ it is kind of misleading. The thing is… dangerous and toxic mold is not just black, it can be many different colors. Toxic molds can appear to be green, yellow, brown, and black.
All molds have the potential to cause irritation and allergy symptoms. However, some molds can also cause much more dangerous health problems. Some molds, but not all, produce mycotoxins. Not all molds are toxic, but many are. Mycotoxins can cause health problems ranging from poisoning to cancer.
So, What is a Mycotoxin?
Mycotoxins, literally ‘fungus poison’ in Latin, are secondary metabolites that can be produced by molds, and are not living organisms. Mycotoxins are a byproduct of mold. Not all mold spores produce mycotoxins, but some do. So the molds that produce mycotoxins are the ones that could be categorized as toxic or poisonous.
So, where is the line between an allergic mold and a toxic mold? That line is defined by the presence of mycotoxins, and is NOT defined by color. Mycotoxins are invisible and cannot be detected just by looking at the mold growth.
What Do Mycotoxins Do?
These chemical substances can cause many health problems ranging from mild to severe. Even if you are not allergic to mold, you can be affected by mycotoxins.
Mycotoxins can be absorbed by the body in a number of ways including: through the skin, the airways (inhalation), and through the intestinal lining (ingestion). Detrimental health effects caused by mycotoxins can range from “acute poisoning to long-term effects such as immune deficiency and cancer.”2 Chronic disease sufferers, such as people with immunosuppressive disorders or underlying lung disease may be more sensitive to molds and mycotoxins in their environment.4
One of the main ways people and pets become poisoned by mycotoxins is through eating contaminated foods. Foods such as apples, cereal grains, coffee beans, nuts, spices, dog and cat food, and more can become contaminated with fungi that produce mycotoxins.
To learn more about mycotoxins in foods check out the World Health Organization’s article: Mycotoxins.
Did you know that toxic mold can affect your pets as well? To learn more about how mold affects your pets check out our article: Mold and Pets – 10 Things You Most Likely Didn’t Know.
Mold on Windows – Prevention
Prevention is worth nine-tenths of the cure they say! To keep mold away:
- Dust windows regularly (at least monthly) with a HEPA vacuum.
- Wash windows at least twice a year inside and out to prevent dust buildup and mold growth.
- Check windows for leaks at least 3-4 times a year to prevent mold growth.
- Replace windows that have continuous moisture problems.
Mold can grow on both aluminum and wooden windows. Have you ever seen windows that just stay moist between the panes? If there is enough dust in that thin space, mold can even grow inside the glass!
Wooden Windows
For wooden windows, using a high-gloss paint to protect the wood is important. High-gloss paint helps moisture evaporate faster and make cleaning windows easier. Wooden windows are also more susceptible to holding moisture between the panes of double hung windows. Aluminum windows are easier to keep clean, because mold can’t grow inside the frame.
Replace Windows with Moisture Problems
Windows that stay moist are a disaster waiting to happen. When windows stay moist, that moisture can move into the space surrounding the window. When that happens, much more work needs to be done! Mold can start to grow in the drywall surrounding the window. If you have moist windows, they are much more likely to grow mold. Replace old windows that continuously have moisture problems.
Mold on Windows – Cleaning
If you’re reading this article, you probably already have mold on your windows, and you’re looking to get rid of it! Removing mold can be a DIY project, but it’s a good idea to know when to call the professionals. Whether you choose to DIY or professional help, we want to help you get back to living your best life in a clean mold-free home!
Step 1 – Get a Professional Mold Inspection
Mold is a difficult thing to find. Step 1 should be a comprehensive mold and indoor air quality inspection. A comprehensive inspection includes ALL the areas of your home from the top of the attic to the basement or crawlspace and everywhere in between. If you have mold in one place of your home, you are more likely to have it in others.
The company you choose for the inspection should offer a comprehensive mold inspection that you pay for, not hand over a price without truly investigating the problem. Your inspector should define the extent of the necessary work and what may or may not need to be done. The inspector should talk you through all your options and tailor a plan that fits your needs and your budget.
Check out our post: Do You Have Mold? How to Choose Between a Paid or Free Mold Inspection to learn about a problem we solved for a homeowner that was NOT mold.
Step 2 – Can I clean the mold myself or do I need a professional?
Mildew (mold’s cousin) is usually easy to remove and is easily a DIY project. Mold however is a different story.
You may wonder if professional help is really necessary. Customers often ask us, “Can I clean the mold myself or do I need a professional?” Our answer depends several factors including:
- how extensive the mold problem is
- what building materials, furnishings, and belongings are affected
- where the mold is located
- whether or not you mind being in confined spaces such as your crawlspace, basement, or attic
If you’re familiar with our blog, you know that the first thing to do when cleaning mold is to fix the moisture problem that led to the mold growth. Until you fix the moisture problem, mold will continue to grow and spread. That ‘weeping window’ has to be replaced to stop mold from coming back.
Mold is great at hiding in hard to detect locations such as in drywall and insulation. If the area of mold covers more than about 10 square feet, there is a good chance the mold problem is more than an isolated issue.
If the area of mold is less than 10 square feet, you may be able to handle it yourself. To get all the details check out our post: Black Mold vs Mildew – 7 Common Misconceptions and When to DIY. We give you all the details on how to safely clean the mold or mildew yourself.
KNOW WHEN TO CLEAN AND WHEN TO CALL
It’s not hard to take care of mold as a homeowner, but it’s a good idea to know when to call in the pros. If you smell a musty odor in your home you can’t identify, or have health problems associated with mold, it’s time to call in the professionals. If an area of mold covers more than around 10 square feet, there is a good chance the mold problem is more than an isolated issue, and it’s time to call the professionals.
Especially if you don’t live in our service area, check out our post: How to Choose the ‘Best’ Black Mold Removal Company. We help you know all the questions to ask the mold removal company and give you all the correct answers.
The company you choose should know all the answers to the questions in our article. Don’t get scammed! Get smart! Always ask a lot of questions before hiring anyone to work on your home.
THE BRANCH DIFFERENCE
At Branch Environmental, we see each mold inspection as an in-depth investigation, not an opportunity to hand over a guess-based estimate of work. If you think you may need a mold inspection, get in touch with us, and we’ll get down to the source.
Call Branch Environmental. We’re experts not only at mold removal, but at determining and remediating the underlying causes. From hidden mold sources to major contaminants, we can identify exactly what is going on in your home and rid it of environmental toxins, often for good.
Branch Environmental – Because nobody should live or work in a building that makes them sick.
For more information go to:
- Signs of Mold in Your House and What to Do about Mold – Branch Environmental
- Black Mold in the Bathroom – Everything You Need to Know
- Black Mold vs Mildew – 7 Common Misconceptions and When to DIY – Branch Environmental
- Mold Allergy Avoidance – How to Stay Well – Mold Allergy Inside & Outside – Branch Environmental
- When Mold Is Worse Than Allergies – Branch Environmental
- Mycotoxins – World Health Organization (WHO)
- Basic Facts about Mold and Dampness – Center for Disease Control (CDC)
- Mold and Pets – 10 Things You Most Likely Didn’t Know – Branch Environmental
- The Health Effects of Black Mold – on Adults, Children and Pets – Branch Environmental
- What’s that musty smell? MVOC’s – Branch Environmental
- Do You Have Mold? How to Choose Between a Paid or Free Mold Inspection – Branch Environmental
- Dust Mites – Branch Environmental
- Water Leaks Contribute to Mold and Health Problems – Branch Environmental
- How to Choose the ‘Best Mold Removal Company Near Me’ – Branch Environmental
- 10 Things You Need To Know Today About Black Mold From a Water Leak – Branch Environmental
- Cleaning Mold: DIY v. Professional – Branch Environmental
- Mold Exposure Symptoms – Branch Environmental