If you've found mold in your home, one of the first things you may be offered is a mold test. Sometimes testing is useful. Often, it isn't necessary. Here's an honest look at what the public health agencies say, and when testing might actually be worth it.
The CDC's guidance is direct: "CDC does not recommend mold testing." Its reasoning: health effects of mold vary from person to person, so sampling can't tell you whether someone will get sick; good sampling can be expensive; and there are no set standards for what is and isn't an acceptable amount of different kinds of mold in a home. The CDC's conclusion: "The best thing you can do is to safely remove the mold and prevent future mold growth" (CDC).
The CDC also says you do not need to know the type of mold to remove it. If you see or smell mold, remove it and fix the moisture problem.
The EPA's guidance similarly emphasizes that the key to mold control is moisture control, and that if mold is a problem, you should clean up the mold and get rid of excess water or moisture (EPA).
Testing isn't useless; it just isn't a first step for visible mold. Situations where homeowners and professionals often find testing or professional assessment helpful include:
A good mold inspection focuses on moisture, not just mold:
If sampling is recommended, ask:
Some homeowners prefer to hire an independent inspector who doesn't also perform remediation, so the person diagnosing the problem doesn't profit from the cure. That's not required, but it's worth considering for larger jobs.
See our page on black mold for more on why color alone doesn't determine risk.
Persistent musty smell in canyon homes. In Mill Valley and Larkspur, below-grade walls and shaded rooms can harbor hidden moisture. Moisture investigation is usually more useful than air tests.
Closed-up vacation homes. In Stinson Beach and West Marin, musty odors in a reopened house often point to humidity rather than a hidden leak. See our vacation home guide.
Buying a home. Many Marin homes are older, with crawlspaces. See our guide to mold questions to ask when buying a Marin home.
If you can see or smell mold, you generally don't need a test to know you should remove it and fix the moisture. Testing can help in specific situations. If someone recommends it, ask why and how results will change the plan.
If you decide testing makes sense, a few things make the results more useful. Air samples are usually compared with an outdoor sample taken at the same time, since mold spores are always present outdoors. Surface samples show what's growing on a particular spot. A single sample captures one moment and can vary with weather, activity and ventilation. Ask the inspector to explain the results in plain language: what was found, how it compares with the outdoor baseline, and, most importantly, what they recommend doing. Because the CDC notes there are no set standards for acceptable indoor mold levels, be cautious of reports that use numbers alone to justify large projects without identifying a moisture source.
Submit a request to connect with an independent local mold inspection or remediation provider. Ask them about their approach to moisture investigation and testing.
No. The CDC says it does not recommend mold testing and advises removing mold and fixing moisture regardless of type.
Possibly for suspected hidden mold, real estate transactions, post-remediation verification, or disputes.
The CDC says you don't need to know the type to remove it.
To compare indoor results with the outdoor baseline, since spores are always present outside.
Given the CDC's position on testing, many professionals suggest focusing on finding and fixing moisture instead.
Consider an independent inspector, especially for larger jobs, and ask about their methods.
This article is general information, not legal, insurance or medical advice. Sources are linked in the text.