7 min read

# Mold Testing: What Actually Works (And What Doesn’t)

You buy a $15 petri dish kit, leave it on the counter, and it grows fuzz. Of course it does. Now you are scared, confused, and still no closer to the question that matters. Is your home actually a problem.

It makes sense to want a simple answer. It sounds like you are trying to do the responsible thing and still feel stuck. Mold testing can help, but only when the method matches the question you are asking.

This guide shows you the tests that actually tell a useful story, the ones that do not, and how to choose a path that protects both your health and your budget.

Those numbers come from the EPA-developed ERMI research and large reviews on dampness and health, including [Vesper, 2007](https://doi.org/10.1289/ehp.9849), [Mendell, 2011](https://doi.org/10.1289/ehp.1002410), and [Fisk, 2007](https://doi.org/10.1111/j.1600-0668.2007.00475.x).

## What mold testing can and cannot tell you

Mold testing is not a diagnosis. It is data. It can tell you what types of mold are present in dust or air, and it can hint at whether your home looks more like a typical building or a water damaged one. It cannot tell you how your body will respond or how sick you should feel.

That is why good testing focuses on two things at once.

1. **What is in the environment.** Dust, air, or material samples.
2. **Where the moisture is.** Moisture mapping and inspection to find the source.

If you skip the second part, you can end up with a lab report and no idea what to fix. If you skip the first part, you can end up with a visual inspection that misses hidden growth. You want both, even if you start small.

## The science behind the most reliable tests

### ERMI and DNA based dust testing

ERMI stands for Environmental Relative Moldiness Index. It was developed to compare homes using a standardized DNA based method called MSQPCR. The lab tests a dust sample for a panel of 36 mold species and calculates a score that places your home against a national reference database [Vesper, 2007](https://doi.org/10.1289/ehp.9849).

Why dust. Dust collects spores and fragments over time, which smooths out the daily swings that make air samples tricky. It is not perfect, but it is a more stable snapshot than a single five minute air draw.

ERMI is best for screening and for comparing one home to another, not for locating the source. If your score is high, you still need an inspection to find the moisture.

### HERTSMI 2 for post remediation checks

HERTSMI 2 is a simplified score that focuses on a small set of species associated with water damaged buildings. Many clinicians use it for post remediation or safe housing decisions. It does not replace ERMI, but it is easier to interpret if your goal is confirmation rather than broad screening. For a deeper explanation, read [ERMI testing explained](/vault/ermi-testing-explained).

### Professional inspection with moisture mapping

A good inspector tracks moisture, because moisture is the cause. Thermal imaging, moisture meters, and careful visual inspection can locate hidden leaks behind walls, under floors, and inside HVAC systems. This matters because remediation plans should be built around the source, not just the surface.

If you want to understand where mold hides before you test, start with [Hidden mold: where to look](/vault/hidden-mold-where-to-look).

## Tests that sound helpful but usually are not

### Petri dish home kits

Those settle plate kits mostly prove that mold exists in your air. It does in every building, even very clean ones. They cannot tell you whether the level is abnormal or whether a hidden source is present. They are dramatic, not diagnostic.

### Air cassette testing alone

Air testing can be helpful when done alongside inspection and multiple samples. Alone, it is a narrow snapshot. Spore levels swing with humidity, activity, and HVAC cycles, so a single air test can miss hidden problems. If an inspector recommends air testing, ask how it fits into the larger plan.

## How to choose the right testing path

Think of this as a ladder. You can start on a lower rung and climb if the data suggests it.

## What a good inspector looks like

A solid inspector is your guide, not your salesperson. Use this as a quick filter when you are calling around.

• Holds an independent certification like ACAC or equivalent
• Is not tied to a remediation company
• Uses moisture meters and thermal imaging, not just air tests
• Provides a written report with photos and specific locations
• Explains the plan and answers questions without pressure

If you need help understanding inspection results, bookmark [Testing your home for mold](/vault/testing-your-home-for-mold).

## Common testing questions, answered like a human

### Should I test before I see any mold

Yes, if you have symptoms that improve away from home or a known water event. Hidden growth is common, and moisture can linger behind surfaces. Testing can give you clarity before you open walls or spend on remediation.

### Can I use ERMI as proof for landlords or insurance

Sometimes it helps, but it is not always accepted as a legal standard. Pair it with a professional inspection and clear photo documentation. If you are navigating a claim, see [Filing insurance claims](/vault/filing-insurance-claims).

### If my ERMI score is high, does that mean I am sick

No. It means your environment looks more like a water damaged building compared to the reference database [Vesper, 2007](https://doi.org/10.1289/ehp.9849). Your symptoms depend on susceptibility, exposure, and timing. Still, a high score is a strong reason to investigate further.

### What if my test is low but I still feel bad

That happens. Mold is not the only exposure that can cause symptoms. You may need to look at ventilation, VOCs, or other indoor air issues. The [Indoor air quality guide](/vault/indoor-air-quality-guide) can help you zoom out without dismissing your experience.

## When to test after water damage

If you have a leak, overflow, or flood, time matters. Mold can grow quickly when materials stay damp. Large reviews show dampness is common and linked to respiratory symptoms, which is why drying quickly and testing when needed is so important [Fisk, 2007](https://doi.org/10.1111/j.1600-0668.2007.00475.x), [Mendell, 2011](https://doi.org/10.1289/ehp.1002410).

If you are unsure what counts as a serious water event, read [Water damage restoration: what to know](/vault/water-damage-restoration-what-to-know).

## Your quick action plan

Use this to turn information into a plan you can actually follow.

• Write down your goal and your budget before you order anything
• If screening, start with ERMI or HERTSMI 2 dust testing
• If you need a source, hire a qualified inspector with moisture mapping
• Document any visible stains, odors, or past leaks with photos
• Use results to plan remediation and retest after work is complete

If you want to go deeper, these guides will support the next step:

– [ERMI testing explained](/vault/ermi-testing-explained)
– [Testing your home for mold](/vault/testing-your-home-for-mold)
– [Remediation: what to expect](/vault/remediation-what-to-expect)
– [Mold safe housing guide](/vault/mold-safe-housing-guide)

## Sources

– Vesper SJ et al. Development of the Environmental Relative Moldiness Index for homes in the U.S. [Vesper, 2007](https://doi.org/10.1289/ehp.9849)
– Mendell MJ et al. Indoor dampness and mold as indicators of respiratory health risks. [Mendell, 2011](https://doi.org/10.1289/ehp.1002410)
– Fisk WJ et al. Meta analyses of indoor dampness and respiratory effects. [Fisk, 2007](https://doi.org/10.1111/j.1600-0668.2007.00475.x)