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Detecting Indoor Allergens: A Guide for Home Inspectors

by Jamie Coupaud, SimpleLab

The 1960s rambler looked perfect on the outside: a five-year-old roof, clean exterior paint, and a well-maintained lawn. The inside was just as clean and show-worthy. But as soon as the inspector entered the soon-to-be nursery, a faint odor prompted him to dig deeper.

You see, when the call came in for this inspection, the buyers—a young couple and their two small children—expressed concern about the age of the house and potential allergens. Their toddler had recently been diagnosed with a wide range of environmental allergies, and in a hot housing market, they were forced to reconcile budget and health. Armed with this background knowledge, the inspector understood that not all allergen-related hazards are straightforward and obvious.

Trusting instinct, he gathered samples from the room’s surfaces. Days later, the verdict came back: elevated levels of Felis domesticus, or cat allergen, concentrated in the nursery. The listing had claimed that the home was “pet-free,” but the wall-to-wall carpet and supply vents still held years of dander. Armed with data, the buyers negotiated for professional duct cleaning and a credit for new flooring before signing the papers.

Most clients expect inspectors to find leaky roofs, shaky decks, and bad wiring. But for some home buyers, what’s floating in the air or buried in the carpet is just as concerning as structural issues. Indoor allergens, tiny bits of mold, dust, and dander, can fly under the radar and easily turn a dream home purchase into a nightmare. You don’t have to be an allergist to help buyers identify these issues. You just need to know where allergens like to hide and how to talk about what you find.

Why Should Inspectors Care About Indoor Allergens?
A healthy house sells faster and at a better price. If a buyer’s toddler starts coughing during the walkthrough, you can bet they’ll remember. By pointing out conditions that allow allergens to thrive, such as damp basements, old filters, or signs of pests, you add real value to the inspection and overall home-buying experience.

The Big Five Offenders
Here are some common indoor allergens that you should keep on your radar:

1. Mold Spores thrive in damp spots: behind drywall, under sinks, around window sills.
2. Dust Mites love warm, soft spaces like mattresses, carpets, and even stuffed toys.
3. Pet Dander are tiny skin flakes from cats and dogs that cling to fabric and ducts.
4. Cockroach Droppings and body parts that collect in kitchens and crawlspaces.
5. Pollen brought indoors by sticking to clothing and coming through open windows. These particles settle on shelves and window ledges.

Red Flags You Can See (or Smell)
Allergens themselves are microscopic, but the conditions that create them can be visible. Visual red flags may include condensation on windows, water stains on ceilings, pest droppings, or peeling paint. These are all signs of excess moisture that make a home accommodating to mold growth. Musty or ammonia- like odors can indicate hidden mold or pest problems.

Use your usual tools: moisture meters, infrared cameras, as well as your own eyes and nose. Note anything that looks or smells off.

Five Ways to Cut Allergen Levels
Clients appreciate quick wins. Offer these tips when a sale is on the line or when advising new homeowners.

1. Run exhaust fans in bathrooms and kitchens for at least 20 minutes after use.
2. Keep humidity between 30-50 percent with dehumidifiers or increased ventilation.
3. Change the home’s HVAC filters every 60-90 days (more often with pets).
4. Seal gaps that let pests in, and check crawl spaces, basements, and attics, as they are often overlooked spaces where critters live.
5. Vacuum with a HEPA filter and wash bedding in hot water weekly. 

These suggestions turn a problem report into an action plan. 

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When to Mention Lab Testing
Your eyes, nose, and instruments may be enough to sense a problem, but if your clients want certainty, sending samples to a lab is the best way to accurately identify the culprit. Especially in cases where you see a mold‑like substance or evidence of excess moisture, your buyers will likely want more certainty.

In those instances, explain that air or surface samples can confirm what’s growing and how severe the issue might be. Providing test kits for these cases is a service that will set you apart from other inspectors. Some lab testing companies will allow you to keep test kits on-hand and directly provide them to clients. If you choose not to provide test kits, you can point your clients to a qualified testing service if they’re interested.

Talking About Allergens in Your Report
When it comes to communicating potential allergen risks in your inspection report, it’s important to use everyday words that your clients know and understand so they can quickly assess the risk and make informed decisions moving forward. Lead with what you measured or observed and use factual readings, such as lab results, if available. Avoid alarmist interpretations of the situations and do not offer medical advice. The next practical steps if allergens are detected could include improving ventilation, consulting a certified remediator, or replacing carpet. All these steps offer clients a reasonable course of action, rather than adding to fear or diagnosing medical conditions.

Make sure you document your methods. One short line such as “samples collected with sterile swabs; chain of custody maintained,” shows professionalism and increases client confidence.

Lastly, closing on a positive note to remind buyers that most allergen problems are fixable can help keep deals moving forward.

Quick Field Checklist
Before you leave the property, run through this mental list:

• Smell test: any musty or chemical odors?
• Moisture check: are there elevated readings in bathrooms, basements, or attics?
• Ventilation: are exhaust fans working, are there clean filters, clear dryer vent?
• Visual sweep: are there stains, peeling paint, fuzzy growth, signs of pests on the property?
• HVAC: how is the filter condition? Any dust on vents, drip pan leaks? 

If one or more boxes are checked, mention allergen risks in your summary.

Closing Thoughts
Indoor allergens can be just as detrimental to a home purchase as a cracked foundation if they lead to long-term health issues for occupants. By watching for moisture, ventilation, and cleanliness issues, you help clients avoid costly surprises. That’s good for their health and your reputation. So next time you walk through a front door, pay attention to those subtle and often hidden signs of allergens. A few extra minutes of attention can help your clients breathe easier and send more referrals your way. 

About the Author
Jamie Coupaud heads Media Communications at SimpleLab, a leading platform for professional laboratory testing. From producing an online water quality course to creating social media content, she has educated consumers and professionals on the ins and outs of environmental testing since 2021.

Published by OREP Insurance Services, LLC. Calif. License #0K99465