How to Test for Mold at Home: 6 Steps (Texas Guide)

Mold is everywhere in small amounts. The EPA says spores are naturally present in both indoor and outdoor air, and the CDC says "there is always some mold around". So the goal of a home mold test isn't to find out whether any mold exists. It's to find out whether mold is growing in your house, and where.

Growing mold needs moisture. NIOSH puts it plainly: any mold growing in buildings indicates a problem with water or moisture. That's why the steps below focus on moisture first and lab tests last.

There's also no number to test against. The EPA says there are no EPA regulations or standards for airborne mold contaminants, and the CDC says there are no set standards for what is and what is not an acceptable quantity of mold in a home. A lab result needs a trained person to interpret it.

Step 1: Look for visible mold

Walk the house with a good flashlight. The CDC says mold can look like spots of many different colors. Check the places water collects:

• Bathrooms: around tubs, showers, toilets and under sinks (see mold in the shower)
• Kitchen: under the sink, behind the fridge and dishwasher
• Exterior walls and window frames, where condensation forms
• Ceilings under bathrooms or below the roofline
• The air handler closet and around AC vents
• Garage walls and any room that took water in a storm

If you find growth, you've answered the main question. The EPA says in most cases, if visible mold growth is present, sampling is unnecessary. Our guide to signs of mold in your house has photos and descriptions.

Step 2: Use your nose

A musty smell is one of the best clues you have. The EPA's mold course says damp or musty odors suggest that water is or was present and mold growth is likely. The CDC adds that mold can smell musty.

Smell is strongest in closed spaces. Open closets and cabinets that have been shut for a while, and sniff near baseboards, carpet edges and the return air grille. A smell with no visible source is a reason to keep looking; the EPA calls out a building that smells moldy, but you cannot see the source as a sign of hidden mold. More in mold smell in your house.

Step 3: Find moisture with a moisture meter

A pin or pinless moisture meter is the most useful mold-hunting tool a homeowner can buy. The EPA says many investigators use moisture meters to find wet areas where mold may be growing, and that these meters measure the moisture in many types of building materials.

How to use one:

1. Take a baseline reading on a dry interior wall in a room with no leaks.
2. Scan drywall below windows, around plumbing walls, under sinks and along baseboards on exterior walls.
3. Compare. A patch reading much higher than your baseline points to water inside the wall, even if the paint looks fine.
4. Re-check the same spot a few days later. Readings that stay high mean an active leak, not a one-time spill.

The EPA notes a moisture meter can help an investigator locate hidden areas of mold growth, because the mold follows the water.

Step 4: Check indoor humidity

A cheap humidity gauge tells you whether the whole house is damp. The EPA says humidity gauges may be useful for checking or monitoring humidity throughout the building, and recommends keeping indoor humidity below 60 percent (ideally between 30 and 50 percent). Houston and Corpus Christi summers make that hard without a working AC and, often, a dehumidifier.

Step 5: Look for hidden mold carefully

Mold doesn't need light. The EPA lists hidden spots such as the backside of drywall, wallpaper, the top side of ceiling tiles, the underside of carpets and pads, and damp areas behind walls and in crawlspaces.

Go slowly here. The EPA warns that investigating hidden mold requires caution since disturbing moldy areas may spread mold throughout the building. Peeling back wallpaper or cutting into a wet wall can release a burst of spores. If your meter says a wall is wet and you smell mold, that's often the point to stop and call a pro. Professionals sometimes use a borescope, an optical probe inserted through a small hole drilled into a wall, to look without tearing the wall open.

Step 6: Decide whether a lab test is worth it

Only now does a kit or lab sample make sense, and only for a specific question. Here's how the options compare:

Table: home mold test options and what each is good for.

Our mold test kit guide covers each kit type, lab fees and what results mean.

Many people search for a way to test for toxic mold. Here's what the science says:

• "Toxic mold" isn't a kind of mold. The EPA says "black mold" is not a species or specific kind of mold, and neither is "toxic mold."
• Some molds can make toxins under some conditions, but no one can tell whether a mold is producing mycotoxins just by looking at it.
• NIOSH says that for molds that can produce toxins, the molds themselves are not toxic or poisonous, and they should be treated like other indoor molds.
• The CDC says it is not necessary to determine what type of mold you may have and that all molds should be treated the same with respect to potential health risks and removal.

A lab can identify Stachybotrys (the mold usually called "black mold") on a swab. But the CDC says no test exists that proves an association between Stachybotrys chartarum and particular health symptoms. Finding it doesn't change the plan: fix the moisture and remove the growth. See our black mold guide.

If you or someone in your home feels unwell, talk to a doctor. The CDC says the health effects of mold are different for different people, so you can't rely on sampling to judge your risk. A doctor diagnoses illness; a mold test doesn't. Our black mold symptoms guide covers what the CDC says about health effects.

In Texas, mold testing done for hire is a licensed job. State law defines mold assessment to include an inspection, investigation, or survey of a dwelling and the collection or analysis of a mold sample, and says a person may not perform it unless the person holds a mold assessment license. You can test your own home under the owner and tenant exemption.

Call a licensed mold assessment consultant when:

• You smell mold or get high meter readings but can't find growth. The EPA says investigating hidden mold can be difficult and may require a professional.
• The area looks large. The EPA suggests professional help when mold growth covers more than 10 square feet. In Texas, the small-job exemption covers only contamination of less than 25 contiguous square feet, and licensed remediation follows a project-specific protocol written by an assessment consultant.
• You had a flood or hurricane damage. After Hurricane Beryl, Texas DSHS advised replacing flood-damaged porous wallboard from at least 12 inches above the waterline. See mold after a flood in Texas.
• You need a document. For an insurance claim, a landlord dispute or a home sale, a licensed consultant's signed report carries weight. Consultants prepare mold assessment reports, including analysis and interpretation of sample results. Renters should read mold in your apartment in Texas.
• Mold was removed and you want proof it worked. Only a licensed consultant can run the post-remediation assessment and clearance. See mold clearance testing.

What a professional mold test costs

Table: professional mold testing cost (national, not Texas-specific). For more, see mold testing cost and is mold testing worth it.

Hire the tester and the remover separately

Texas law says a license holder may not perform both mold assessment and mold remediation on the same project. That keeps the company that tests your house from profiting off the removal it recommends. Hire a testing company for the assessment, then a separate removal company if you need one. We explain the rule in why mold testing and removal must be different companies.

Before you hire, run the company and the person through our Texas mold license check. Licensed testing companies by city: Houston, Dallas, Austin, San Antonio, Fort Worth, or all of Texas.