ERMI Test vs Air Sampling: Which Mold Test Fits?

ERMI stands for Environmental Relative Moldiness Index. EPA scientists created it. According to the EPA fact sheet:

• Researchers analyze the DNA from mold found in dust samples collected from a home and compare it to the ERMI scale.
• The scale was built from over 1,000 homes representing housing from across the continental U.S., part of HUD's American Healthy Homes Survey, using 36 indicator molds.
• The DNA method behind it is called Mold Specific Quantitative PCR (MSQPCR).
• The scale ranges from a low of approximately -10 to a high of about 30. A higher number means the home's dust looks moldier relative to that national sample.

In practice, a dust sample from the home goes to a lab that runs the DNA analysis and reports a score. What that score means for your house is the bigger question.

The EPA won't vouch for it outside research. Its fact sheet says ERMI has been peer reviewed for research purposes but has not been validated for non-research purposes, and that for this reason, EPA does not recommend the routine public use of ERMI in homes, schools, or other buildings.

On accuracy specifically, the EPA says that because the approach has not been validated through a multi-lab study, we cannot comment on the accuracy of information obtained from others using ERMI. It adds that inspection for water damage and mold remain the key to current EPA guidance.

The EPA's research page, updated in 2026, still describes ERMI as a research tool developed by EPA scientists for estimating mold contamination.

The 2013 Inspector General report

In 2013 the EPA's Office of Inspector General looked into ERMI after a complaint. Its report was titled Public May Be Making Indoor Mold Cleanup Decisions Based on EPA Tool Developed Only for Research Applications. It found that:

• Firms were using the tool although the EPA had not validated the tool for public use.
• The EPA said it considers MSQPCR and ERMI to be research tools not intended for public use.
• Advertising by one current and one past licensee could mislead the public into thinking that these research tools are EPA-approved methods.

The OIG recommended that the EPA finalize a fact sheet on indoor mold, MSQPCR and ERMI to tell the public these tools had not been validated for public use. The fact sheet quoted above is that document.

Bottom line: An ERMI score is not an EPA-approved verdict on your home. If someone tells you a high ERMI score means your house is "toxic" or that you must remediate, ask what visible mold or moisture problem they found.

A mold air test (often sold as an "air quality test for mold") pulls air through a collection device so a lab can identify and count the mold spores in it. Bob Vila's test kit review describes the basic idea: the pump pulls in air for a specified amount of time.

There are two broad lab approaches. The Minnesota Department of Health explains that some methods can identify a portion of the types of live (viable) molds, while other methods are better able to characterize the total amount of molds in a sample.

Spore traps

A spore trap is a cassette that catches airborne particles, including spores, for a lab to examine directly rather than growing them in a dish. That makes it a non-culturable sample. Texas lab licensing rules reflect this: one path to a lab license covers labs that analyze only non-culturable samples, and another requires analysts with three years of experience as a mold microscopist. See mold testing labs in Texas.

Why outdoor control samples matter

Mold spores are everywhere. TDLR's consumer sheet says spores are always present at some level in the air and on surfaces all around us. So an indoor number on its own doesn't mean much.

That's why air sampling is read against an outdoor sample taken at the same time. The EPA's mold course says that after remediation, the types and concentrations of mold in indoor air samples should be similar to those in the local outdoor air. It lists "outdoor control samples may be omitted" among common sampling problems. Even consumer kits follow this logic: one kit in Bob Vila's review charges $39 per lab test, including a required outdoor control sample.

Limits of air sampling

Federal and state health agencies list several:

• It's a snapshot. The EPA says air sampling provides information only for the moment when the sampling took place. Minnesota adds that variability can be especially large for airborne molds.
• A clean result can mislead. NIOSH says short-term results, especially negative findings of mold, may not represent actual exposures.
• No standard to compare against. The EPA says there are no EPA regulations or standards for airborne mold contaminants. NIOSH says there are no health-based standards for mold in indoor air.
• It can't predict illness. NIOSH says short-term sample concentrations cannot be interpreted in relation to health risks.
• It needs expert reading. The EPA says that for someone without experience, sampling results will be difficult to interpret.

NIOSH sums it up: thorough visual inspections or detecting problems by musty odors are more reliable than air sampling.

ERMI vs air sampling: what each mold test measures

Testing earns its cost when the answer would change what you do. The EPA's mold course puts it plainly: unless the results would or could make a change in your plans, you don't need to sample. Good reasons include:

• A musty smell with no visible mold. Sampling may help locate the source of mold contamination.
• Checking that cleanup worked. The EPA says surface sampling may be useful to determine if an area has been adequately cleaned or remediated. In Texas this is the clearance step; see mold clearance testing.
• A dispute or legal matter, where the EPA says you may consider sampling as part of the evaluation.

In Texas, if testing is done before cleanup, TDLR says the licensed consultant should establish criteria for interpreting the test results. TDLR also warns that sample results cannot be interpreted without physical inspection of the contaminated area. That's a good argument for a licensed inspection over a mail-in test. Our how to test for mold and mold test kits guides compare the DIY and professional routes.

If you're testing because someone feels sick, know what a test can and can't do. The CDC says you cannot rely on sampling and culturing to know whether someone might become sick. A doctor diagnoses illness, not a mold test. The CDC advises that individuals with persistent symptoms should see their physician. Our black mold symptoms guide covers what's known.

TDLR treats collecting mold samples as mold assessment, which requires a mold assessment technician or consultant license, and the samples must go to a laboratory licensed under §78.62. The company that tests can't also do the removal on the same project: a license holder may not perform both mold assessment and mold remediation on the same project.

Ask any testing company before you book:

1. What question will the test answer, and how will the result change the plan?
2. Will you take an outdoor control sample at the same time?
3. Which licensed lab will analyze the samples?
4. If you offer ERMI, how do you explain the EPA's position that it isn't validated for this use?

Find licensed mold testing companies in Houston, Dallas, Austin, San Antonio and across the Texas page, and confirm any license with our license check tool.