A gloved hand holding a petri dish filled with mold

Ever catch a whiff of something musty or “earthy” while you’re in the basement doing laundry? Wonder why your child is coughing and sneezing for no apparent reason? Questioning why the rash on your husband’s arm keeps coming back?

It might be that four-letter word every homeowner hates to hear: mold.

While they might not be a huge issue, mold allergies are more common than you think. So if you’re wondering if you might have a mold problem and how to know for sure, keep reading.

But first, as the famous Chinese general Sun Tzu said, it’s important to know the enemy. Let’s take a look at exactly what mold is and why it might be living in your house.

FYI: Some species of mold have bad reputations. Take black mold, for instance. While it is toxic to humans, there is no proof it is any more dangerous than other, similar types of mold. Scientists say that the “toxic mold syndrome” hyped in the media is largely overblown.1

Mold: A Quick Primer

What most people call “mold” is actually an umbrella term for the fungal growth that often occurs on damp organic matter. Scientists have identified over 100,000 types of mold2 and estimate that there might be hundreds of thousands more.

The good news is that the vast majority of molds are harmless, and in small quantities and with limited exposure, most healthy adults will have no problem being around them. However, if your family is especially sensitive to molds, allergic reactions can be triggered.

What’s more, if you have young children, care for elderly family members, or have people in your home that suffer from respiratory illnesses like asthma, the presence of mold in your home can take a significant toll on their health and quality of life.3

How Do I Test for Mold in My House?

Mold spores are everywhere, but it becomes a problem when the presence of mold spores inside becomes higher than the concentration of spores outside.4

How do you know if this is the case in your home? Unfortunately, that’s a difficult question to answer without professional testing equipment and a lab — things most homeowners don’t have access to. Complicating things further is the fact that there are no federal regulations regarding what is considered to be an unsafe concentration of mold or mold spores.5

So even if you were to confirm the presence of high levels of mold in your home, it’s going to be difficult to determine if it’s a problem. But don’t worry; there’s hope.

Pro Tip: It’s almost impossible to determine which type of mold you’re dealing with just by visual inspection alone, but there are about a dozen mold types that show up more often than others. Check out our guide to the most common types of household molds for more information.

There are definitely things you can do for yourself and for your family to test for mold and to make sure no one’s living in a moldy environment.6

First, you’ll need to know what mold looks like. Most mold contamination is unmistakable, but sometimes surface molds can just look like common household dirt and dust. Here’s how to tell if you’re dealing with a mold problem or just a bit of grime:

  • The Q-tip test: Put a Q-tip in some diluted bleach, and dab it on the area in question. If it lightens after a minute or two, it’s mold. If the area stays dark, it’s just dirt.
  • The timing test: Keep track of how quickly it returns after you clean it. If you wipe an area down and it looks the same after a few days, it’s likely mold.

These are great tests for surface mold, but the fact of the matter is mold can grow where you can’t see it. This can cause significant damage to your home and your finances. Some tests for determining if you have mold in unseen places include the following:

  • The screwdriver test: If you know mold was present on a surface, you might have a deeper problem. If possible, probe the area with a screwdriver or other thin, sharp instrument. If the material behind the surface feels spongy or crumbles, you’ll know things have begun to rot.
  • The carpet test: Carpeting is a safe haven for molds, and mold tends to grow underneath before you’ll see it on the top. While it’s not feasible to pull your carpet up every few months and have a look, you should if you have reason to suspect mold might be growing underneath (“earthy” odor?) or if you recently had a water leak. Carpets that are below ground level, like in a finished basement, are especially susceptible to mold.7
  • The ductwork test: If you’re seeing mold on a ceiling and there’s no obvious leak anywhere, you’ll want to inspect your ductwork and registers. Warm, moist air — like the air in your attic — will condense and form water on ducts that carry the cold air from your AC unit. If they are poorly insulated or missing a vapor barrier, that condensation will cause mold.
  • The smell test: If you’re noticing a musty smell that doesn’t have a clear source, you might have mold in your HVAC system. You likely won’t have the tools to inspect it yourself, but if all other options have been exhausted, you might want to have your system inspected and cleaned.

Mold needs four things to grow: oxygen, the right temperature range, organic material, and moisture.8 That last one is the trickiest for families to deal with. There are many reasons why areas of your home might become damp, but if you can remove the moisture, you’ll get rid of your mold. This is one of the most effective tests for preventing mold:

  • The leak test: If you suspect there might be mold in your home, trace your plumbing as best you can. Check pipe joints, fixtures, and junctions for leaks by turning on your water and seeing if moisture accumulates anywhere. You’ll also want to check your windows for signs of water intrusion and get up in your attic to make sure water isn’t getting in immediately after a heavy rainstorm. Remember, water can travel in any direction when it’s wicking through absorbent material, so mold might actually be growing some distance from the leak itself.

Now with all this in mind, you might have heard about mold test kits that are available for purchase. These are also an option, but let’s explore why they might not be as effective as you think.

Using a Commercial Mold Test Kit

There are several commercially available mold test kits on the market that can give you a pretty good idea if mold spores are present in your home. If you want to go this route, here’s what you’ll need to do:

  • Step 1: Purchase a mold test kit. These are available from online retailers and at hardware stores. They typically cost around $40, but some are more expensive than that.
  • Step 2: Close off the space you want to test. Close doors and windows, and shut off the area as best you can to external factors. This will give you a more accurate read of the presence of mold in the environment.
  • Step 3: Set up your test kit. You’ll probably find a shallow plastic or glass petri dish with a lid. Into that you’ll pour the culture, which promotes the growth of mold spores. Other kits may have multiple petri dishes that are “culture-ready.”
  • Step 4: Leave the petri dish uncovered for about 48 hours in the room you’re testing. Remember to leave all the doors and windows closed, and keep your family from entering the room (if you can help it). The more outside intrusion into the environment there is, the less accurate your test will be.
  • Step 5: Seal the dish and place it in a dark place, like a kitchen drawer, for the time period recommended by the test kit manufacturer. Make sure you use tape to keep the lid affixed.
  • Step 6: Observe the mold that appears in the dish. If there are a few dots of growth, you’re likely in the normal range. If the entire dish is crawling, you might have a problem on your hands.
  • Step 7 (optional): If you want, you can send the dish off for testing to determine exactly what type of mold is present. While this might satisfy your curiosity, most experts — including us — feel it’s unnecessary. If you have high concentrations of mold in your home, you’re going to want to get it removed, regardless of its type.

So that’s how to use a commercial at-home mold test. Here’s a tip: Mold spores are present in every home, so it’s extremely likely that your mold test is going to indicate the presence of mold. The key is being able to differentiate between what’s normal and what’s potentially unhealthy.

Remember, a moderate amount of growth is normal. It’s when the growth looks out of control that you should consider calling in professional help.

Do I Need a Professional Mold Test?

When researching your mold problem, you’re probably going to come across three terms: testing, inspection, and remediation. Let’s break each of those down.

  • Testing: A mold test attempts to identify the specific types of mold spores in the air in your home. This is done by a professional who gathers samples and tests them in a lab. If you already know you have a mold problem, testing is likely unnecessary.
  • Inspection: During a mold inspection, a professional will search your house from top to bottom in search of mold and its source. They will also ask you a lot of questions about the construction of your home, your family’s health, and other factors that might contribute to mold growth. When they’re done, they’ll give you a report and recommendations.
  • Remediation: Mold remediation is the process of removing mold and ensuring that it won’t return. This could be as simple as cleaning surfaces and fixing leaks, or as complicated as ripping out drywall and tearing up floorboards.

Pro Tip: Mold remediation can be a very expensive process, but a general rule of thumb to keep in mind is that it’ll cost between $13 and $30 per square foot of contaminated area.10 Read more about that in our mold remediation cost breakdown.

So now that you know what the pros do, you might be wondering if you can handle the problem yourself. While you’ll probably save some cash doing so, you want to make sure you have the skills and abilities to contend with the problem you’re experiencing.

Can I Clean Mold Myself?

It’s perfectly reasonable to think you can handle your home’s mold problem. If all it takes is wiping down a window sill, it would be senseless to call a professional remediation team. The trick is making sure you know the extent of your problem and making sure the problem is addressed comprehensively.

Pro Tip: Remember that mold can grow in places you can’t see, like beneath floorboards, behind walls, and inside ductwork. Just because you think you’ve cleaned it all up doesn’t mean you’ve solved your mold problem.

Surface-level mold, for the most part, can be handled with commercial antimicrobial cleaners or diluted bleach. Make sure you’re working in a well-ventilated area and you wear the proper protective equipment to reduce exposure, including a mask, goggles, gloves, long sleeves, and long pants. Keep in mind that if you have a mold that’s penetrating, you might need to remove the surface you’re cleaning — like drywall.

Another thing to consider is that the EPA recommends any mold contamination that’s larger than 10 square feet be handled by a professional. If your mold problem is widespread, it might be beyond your ability to remediate it successfully.11

Final Thoughts on Mold Testing

While it’s true that every home has mold to some degree, you don’t want your family living in an unhealthy or unsafe environment. There’s just too much at stake.

Whether you test for mold yourself or have a professional tester, inspector, or both come out to your home, you’re going to sleep better at night knowing there isn’t a dangerous threat growing behind your walls, underneath your floors, or underneath your kitchen sink.

Mold Testing FAQs

Are mold tests expensive?

Commercial, at-home tests you use yourself cost about $40 to $90, while professional mold testing can cost between $300 and $900, depending on the size of the home.

What does mold look like?

Mold usually presents as white, gray, green, brown, gray, or black patches that appear fuzzy or slimy. Some molds, though, can look like common household dust and grime.

Is mold dangerous?

Most molds in small amounts aren’t dangerous for healthy people, but high quantities of mold or long-term exposure can result in negative health outcomes.

How do I know if my house has mold?

Most mold contamination is apparent by visual inspection, but if mold is growing somewhere unseen, it can be identified by a musty, damp, or “earthy” smell.

Can I clean mold myself?

Yes. Most instances of mold growth can be remediated without professional help, but the EPA recommends calling in the pros for contaminations larger than 10 square feet.