Spring Allergies or Mold? How to Tell the Difference Inside Your Home
By Robert Weitz, Environmental Testing Professional, RTK Environmental
If your allergy symptoms get worse indoors, flare up in one specific room or building, or stick around after pollen season, mold is a likely cause. Mold grows where moisture sits, often hidden behind walls, under sinks, in air ducts, and in basements.
The way to know for sure is to test the air and surfaces in the location where symptoms appear. May is National Asthma and Allergy Awareness Month. The Asthma and Allergy Foundation of America has marked the month every May since 1984, timed to peak spring allergy season. It’s a useful moment to look at one of the most overlooked indoor triggers we see in our work: mold.
Every spring, our phones at RTK ring with the same story. People are sneezing, their eyes are itchy, their throats feel scratchy, and they assume it’s pollen. Sometimes it is.
After years of testing homes, offices, and schools, I can tell you pollen is often only part of the picture. Indoor mold is frequently doing real damage to indoor air quality, and most people never think about looking for it.
How can I tell if it’s spring allergies or mold?
The clearest signal from an environmental standpoint is location. Pollen affects you wherever you go. Mold tends to affect you in a specific place. If you feel fine outside but your symptoms flare in one building, one room, or one floor of your house, that pattern points to something in that environment. Mold is a common cause.
Another tell: if you keep your windows closed, take allergy medication, and still feel awful indoors, the source is likely inside the building, not outside it.
What are the symptoms of indoor mold exposure?
Mold exposure produces symptoms that overlap heavily with hay fever, which is part of why it gets missed.
Common signs include:
• Sneezing
• Runny or stuffy nose
• Itchy, watery eyes
• Scratchy throat
• Coughing or wheezing
• Postnasal drip
• Skin rash, or dry, scaly skin
Can mold trigger asthma attacks?
Yes. There is a direct connection between mold and asthma, which is part of why allergies and asthma get awareness focus together every May. If you have asthma and you’re sensitive to mold, exposure to mold spores can trigger your symptoms, and the reactions can be severe.
People describe acute coughing, wheezing, shortness of breath, and chest tightness on top of the usual symptoms. This is a strong reason to know what’s in the air you’re breathing at home and at work.
Why are my allergies worse indoors than outside?
Indoor air pollution is often higher than outdoor air pollution. EPA studies have indicated indoor air pollution can run at least twice as high as what’s outside. Homes are sealed, ventilation is limited, and allergens accumulate.
If your symptoms are worse indoors, the air inside is doing something the air outside is not, and mold is one of the most common reasons.
Why does spring trigger indoor mold?
Warmer weather and higher humidity create the conditions mold needs to grow. Spring also brings melted snow and heavier rainfall, which finds its way in through roofs, foundations, and basement walls. Any winter water intrusion you didn’t notice, an ice dam, a slow roof leak, a damp corner behind drywall, often shows itself this time of year.
Mold can begin growing in 24 to 48 hours once moisture is present. By the time you notice the smell or the symptoms, it has had a head start.
Where does mold hide in a house?
Unlike pollen, which you can see coating cars and windowsills, indoor mold hides. It loves a dark place.
The places we find it most often on inspections:
- Behind walls and inside ceilings, especially anywhere a leak occurred
- Under sinks where slow drips go unnoticed
- Inside HVAC systems, air ducts, and exhaust fans
- Behind drywall installed against concrete basement walls
- Under carpet, padding, gym mats, or floating wood floors
- Inside front-loading washing machines
Why are basements such a common source of mold?
Basements are naturally cool and humid, which is exactly what mold needs. The National Association of Home Builders reports that more than 60% of basements in the Northeast are finished living spaces, so a lot of people are spending time in rooms that are working against them.
A few situations come up again and again on our inspections:
- Carpet or padding installed directly over concrete. Concrete holds moisture and can’t breathe. Cover it, and you’ve created a hidden environment for mold.
- Drywall and wood framing against concrete walls. Heavy rain pushes water in along the path of least resistance, where the wall meets the floor. The bottom of the drywall and framing can be damp within seconds.
- Sole reliance on a sump pump or French drain. These systems work, but they need regular inspection. When they fail unnoticed, moisture builds up.
- Laundry areas, gym mats, and floating wood floors. Heat, humidity, and trapped moisture under flooring create conditions where mold grows out of sight.
Plumbing issues from the floors above end up in the basement, too. A toilet overflow, a pipe break, an ice maker leak, water always finds the lowest point. Water sensors on the basement floor are inexpensive and buy you time to clean up before mold starts.
What humidity level prevents mold?
Keep indoor humidity at or below 50–60% year-round. A dehumidifier in damp areas helps, particularly in basements. Anything above that range encourages mold growth.
How can I prevent mold in my home?
There’s no cure for a mold allergy, but you can change the conditions that allow mold to grow. From an environmental standpoint, this is where most homeowners can make real progress:
- Run a dehumidifier in damp areas and keep it set at 50% humidity.
- Clean bathrooms, including tubs, shower areas, windowsills, and curtains, with a bleach or disinfectant solution at least monthly.
- Run exhaust fans during and after showers, and in kitchens and laundry rooms. Make sure they vent to the outside, and clean them every three months.
- Check under sinks regularly for leaks. Mold grows fast where there’s moisture.
- Keep gutters clear of leaves and debris year-round, and remove organic debris from the yard.
- Skip the basement carpet. It traps moisture and is one of the easiest ways to create a hidden mold problem.
- If you’re finishing a basement, hire a builder who knows basement construction, choose non-cellulose materials, and ensure proper ventilation.
When should I have my home tested for mold?
Test when the pattern doesn’t fit ordinary allergies.
Specifically:
- Symptoms keep coming back in the same room or building.
- You’re medicating without much relief.
- You had a winter water intrusion, an ice dam, a roof leak, a burst pipe, and you’re not 100% sure everything dried out.
- Symptoms persist after pollen season ends.
- You can smell something musty but can’t see anything.
Testing tells you what’s actually in the air and on the surfaces, so you and your doctor can make decisions based on real information instead of guesses.
Should I hire the same company to test and remediate?
No. Hire a mold inspector who only does inspections. If the same company is going to bid on remediation, there’s a built-in conflict of interest, the more they find, the more work they sell. RTK only tests.
May is the month set aside to think about asthma and allergies. Use it.
If you’ve been dismissing symptoms as seasonal year after year, take a closer look at the rooms where you feel worse.
The answer is often in the building itself.
