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How to test for mold in your house

Worried about mold in your home? There are easy ways to test for it
Updated on January 10, 2024
Written by
Jeff Somers
Jeff has been writing for HouseFresh since 2023. He lives in Hoboken, NJ with his wife and their cats, and has published nine novels and more than fifty short stories. In addition to writing for HouseFresh, Jeff also covers topics connected to home ownership for Lifehacker,

Mold is always present in the air and will grow when the right conditions exist.

You can take steps to keep your home mold-free by controlling the humidity and performing regular maintenance.

Mold tests include simple DIY approaches, store-bought kits, and professional testing companies.

Places to test for mold include damp areas or locations of water leaks, HVAC ducts, laundry and kitchen appliances, and mattresses and upholstery.

There’s a reason people react with horror when they see mold growing in their homes—mold is bad news. 

Mold spores in the air can harm your health, and both ‘white’ and ‘black’ mold can be dangerous. Mold can reduce your quality of life and cause real damage, eating away at wood, drywall, and other materials. Mold cleanup and repair can be financially devastating, costing $5,000 on average.

Mold spores are always in the air, and the right environmental conditions will result in mold growth. The key to fighting mold is being proactive:

  • Control the humidity. Relative humidity below 50% inhibits mold growth. 
  • Ventilate. A good-quality air purifier can be effective at reducing mold spores in the air. 
  • Maintenance. Repair leaks promptly and clean the home regularly.

Testing for mold can confirm its presence, identify the species, and pinpoint its source.

Three ways to test for mold in your house

If you suspect you have mold growing in your home, there are several ways to test for it.

1. DIY testing

Mold is often difficult to distinguish from simple dirt, and it can hide behind paint. If you think a discolored spot on your wall might be mold, you can conduct two simple, free tests immediately:

  • Diluted bleach. Mix one part bleach with 16 parts water, then dab some (don’t scrub) on the stained portion of the wall. If the discoloration fades away immediately, it’s probably mold. If it comes back a few days later, it’s definitely mold
  • Screwdriver. Take a screwdriver and push the blade against the surface. If it goes in very easily, your wood has likely been chewed up by mold.

2. Test kits

DIY tests can’t identify the type of mold you’re dealing with or reveal mold you can’t see. For that, you’ll need to purchase a testing kit, which comes in two basic varieties:

  • Surface testing. These test kits require you to scrape or swab surfaces, seal the samples into containers, and then either wait for a reaction or send the samples to a lab for professional testing.

The drawback of these tests is that they only determine the presence of mold on the specific surfaces you test.

  • Air quality kits. These mold tests sample the air to determine whether mold spores are present. Some utilize a petri dish, others utilize an air pump that samples the air in the home and routes it to an internal testing medium.

All these kits can tell you on their own is whether some kind of mold is present in high enough concentrations to be worrying. You will need to send the samples to a lab to discover what kind of mold it is.

Sometimes the lab costs are included in the purchase price of the kits, but you should make sure of this before purchase.

3. Professional testers

A third option is a mold testing professional. They will take air and surface samples and conduct lab tests on them—basically, they do everything a test kit does but on a house-wide scale and with trained, professional experience.

These inspections can be pricey, ranging from $600 to $1,000, depending on the size of your home. See below for more detailed information on mold testing costs.

When to consider professional mold testing

Both the Centers for Disease Control (CDC) and the Environmental Protection Agency (EPA) consider mold testing unnecessary if you can see obvious signs of mold; you should simply clean and treat the affected areas. It is often not worth the price of testing to identify the mold, and there are no standards for evaluating whether mold levels are dangerous.

There are some circumstances where professional mold testing may be needed:

  • After treatment, to ensure that mold regrowth has not occurred. 
  • If you need to identify the species due to a severe health reaction. 
  • If you have not been able to the presence of mold.

If you do contact a professional mold testing service, there are several different kinds of tests they can perform, each with its own price tag:

Type of testWhat’s involvedAverage cost
Swab testSamples collected from surfaces.$200-300
Air cellAir samples collected to determine the presence of spores.$240-$360
HVAC testing addition
An additional air test targeting HVAC ducts and returns.$50-$75

Something to keep in mind. Any lab work required will typically be an additional cost ranging from $50 to $150.

What are the signs of mold (and where to look for them)

Knowing the signs of dangerous mold growth in your home can alert you to a potential problem before it impacts your health and property. Here’s what to look for:

  • Staining. Dark spots on walls, darkened grout (caused by mildew, a form of mold), fuzzy or slimy discolorations on surfaces. 
  • Smell. Musty, earthy smells that are very unpleasant. 
  • Damp areas. Mold requires moisture to grow. 
  • Odd tastes. If food and beverages taste “off” it may be due to mold in your appliances. 
  • Health issues. Sudden respiratory problems or skin rashes may be allergic reactions to mold.

Often, mold manages to grow out of sight in hidden places. There are specific areas of your home you should check:

  • Bathrooms and kitchens are damp spaces where ventilation is often problematic. 
  • Mattresses and upholstery can be ideal breeding grounds for mold because our bodies sweat and provide a warm, moist environment. 
  • Windows with failed caulking and weather stripping allow moisture to build up. 
  • Attics, basements, and crawlspaces tend to be damp and “out of sight, out of mind.” 
  • HVAC and laundry ducting can provide the ideal humid conditions for mold.

Wrapping up

Getting rid of mold starts with being aware of its presence. Testing for mold can be inexpensive and testing kits or professional testing can give you the information you need to protect your property and family.

Once you determine that mold is present, don’t panic! Follow this guide to getting rid of mold and you’ll soon be living a mold-free life.


About the author

Jeff Somers

Jeff has been writing for HouseFresh since 2023. He lives in Hoboken, NJ with his wife and their cats, and has published nine novels and more than fifty short stories. In addition to writing for HouseFresh, Jeff also covers topics connected to home ownership for Lifehacker,