What Are the Symptoms of Unhealthy Air—And How Do I Know If My Home’s Air Is Safe?
- Dan Dearden
- Sep 2, 2025
- 6 min read
Updated: Sep 30, 2025
Response by Dan Dearden, CAFS – Certified Air Filtration Specialist, Essential Air Products Founder, NovusAer Inventor
You can find thousands of articles online about the symptoms of unhealthy air and how to test for it. So why write one more? Because most of those articles only cover a piece of the puzzle. After 48 years of training and real-world experience, I can tell you: indoor air quality is a complex subject, and your home is at the center of that complexity.
Think of your house like a living, breathing organism.
It breathes in and out. Outside air sneaks in through cracks and leaks (infiltration) and indoor air escapes outside (exfiltration).
Its “breathing rate” changes all the time. The number of air changes per hour (ACH) shifts depending on wind, temperature differences between indoors and outdoors, doors opening and closing, fans running, and even how your HVAC system is designed.
It’s constantly absorbing and releasing substances. Every person and pet inside exhales CO₂ and brings in dust and dirt. Cleaning supplies, paints, flooring, and furniture all “off-gas” chemicals.
So when we talk about “air quality,” we’re really talking about a system in constant motion.
There are seven main factors experts watch when evaluating indoor air:
Humidity
Carbon dioxide (CO₂)
Carbon monoxide (CO)
Volatile organic compounds (VOCs)
Particulate matter (PM2.5)
Formaldehyde
Temperature (important, but not usually considered a daily health risk—so we’ll set it aside here)
Let’s go through each one, what symptoms to watch for, how to measure it, and what you can do about it.
Humidity
Healthy Range: 40%–60% relative humidity (RH).
Symptoms of low humidity (<40% RH):
Dry, itchy, flaky, or cracked skin
Nosebleeds and sinus irritation
Extra static electricity
Cracked wood floors or furniture, and damage to musical instruments
Symptoms of high humidity (>60% RH):
Mold and mildew growth (which can trigger allergies, asthma, and other health issues)
How to measure it:
Buy a digital hygrometer (about $10). It gives a simple, accurate RH reading.
Click the Picture to purchase a digital hygrometer from Home Depot
Solutions for dry homes (<40% RH):
Install a humidifier. A whole-home bypass humidifier is inexpensive and low-maintenance (though not always an option). Portable humidifiers are effective but require regular refilling and cleaning. Steam humidifiers are effective but cost more to run.
Weatherize your home. Reducing air leaks lowers the rate at which dry outdoor air replaces your indoor air. The typical home exchanges all its air once per hour (1 ACH). Sealing gaps can reduce this to 0.33 ACH (once every three hours).
Or, jokingly, you could move to a more humid climate. Not jokingly, people with serious dry air health issues sometimes do this.
Solutions for damp homes (>60% RH):
If they don’t already exist, install exhaust fans in kitchens and bathrooms.
Use a Heat Recovery Ventilator (HRV) in moist climates, or weatherize your home in wet climates to help your HVAC system keep up.
Consider a whole-home dehumidifier or portable units for smaller spaces.
Or, again jokingly, move to a drier climate. Again, not jokingly, some people with serious moisture-related health issues choose to move to drier climates. Example: if you were severely allergic to dust mites, you would greatly benefit from moving to a dry climate. Dust mites require moisture from the air to survive.
Carbon Dioxide (CO₂)
CO₂ is a natural by-product of breathing, but in high amounts it becomes a problem.
Symptoms:
Tiredness, headaches, dizziness
Difficulty concentrating or confusion
Severe exposure can cause unconsciousness, seizures, or worse
How to measure it:
Digital CO₂ monitors start around $45.
Click the picture to purchase an air quality monitor from Elitech
Solutions:
You can’t remove people or pets, so ventilation is key.
HRVs (in wet climates) and ERVs (in dry climates) bring in fresh air while recovering heating, cooling, and humidity.
Note: In this case, weatherization can backfire. A too-tight home allows CO₂ to build up.
Carbon Monoxide (CO)
CO is different from CO₂. It’s a toxic, deadly gas created by burning hydrocarbon fuel (like natural gas, wood, or gasoline).
Symptoms:
Headaches, dizziness, nausea, fatigue
Severe exposure: chest pain, confusion, seizures, loss of consciousness, and even death
A real story: I once found a furnace leaking low levels of CO into a home. For years, the family had flu-like symptoms every winter. Doctors said it was just “a virus.” Their husband (away most of the week) never felt symptoms, so no one suspected the furnace. UL-listed CO alarms didn’t help—they don’t alert until CO reaches 30ppm. You could breathe 29ppm daily for years without an alarm sounding.
How to measure it:
Skip the $29 detectors from the hardware store. Get one that alarms at low levels (e.g., Defender LL6270, about $200).
Solution:
Always find and eliminate the source. Sometimes it’s not even from your own home—it could be a neighbor’s car warming up next to your house. Remember: your home “inhales.”
Volatile Organic Compounds (VOCs)
VOCs are gases released from cleaning supplies, paints, flooring, adhesives, furniture, and even vaping. Some are irritants; others can cause organ damage or cancer.
Symptoms:
Eye, nose, and throat irritation
Headaches, dizziness, nausea
Worsening asthma or COPD symptoms
How to measure it:
Harder than other pollutants. Options include home test kits, professional testing, or long-term monitors.
Important: VOCs fluctuate. I once left a monitor in a home where readings spiked every weekend. Turns out, the homeowner’s girlfriend vaped during weekend visits.
Solutions:
Eliminate sources (use low/no-VOC products, replace carpets, seal walls with no-VOC paints).
Ventilate with HRVs or ERVs.
If nothing works, you may need to start fresh with a home built from non-VOC materials.
Particulate Matter (PM2.5)
These tiny particles (2.5 microns or smaller) are linked to serious health risks. The World Health Organization sets the safe threshold at 5 µg/m³ (roughly an AQI, Air Quality Index of 28).
Symptoms:
Short-term: irritation, coughing, wheezing, shortness of breath
Long-term: asthma, reduced lung function, heart disease, stroke, cancer, and even reduced cognitive function
How to measure it:
Use a laser particle counter. Professional ones cost $ 4,000 or more, but good homeowner models cost as little as $36.
To test your HVAC filter efficiency:
Measure particles at the return grille (air going in).
Measure at the supply duct (where air is coming out).
Apply this formula:
1 – (supply ÷ return) = efficiency
Example: 1 – (2.7 ÷ 8.6) = 67% efficient
Solutions:
Use air filters—portable or whole-home.
To tackle infiltration (outside air sneaking in), you need a depressurization duct connected to a whole-home system.
Beware of gimmicks. Many so-called “air purifiers” claim to use ionization or oxidation. To date, no independent tests prove that these work in a home. Luckily, with a $36 laser counter, you can test them yourself.
Formaldehyde
Technically a VOC, but so common in today’s homes, it deserves its own mention. The symptoms, measurement, and solutions are the same as VOCs.
Summary
Thanks to affordable testing tools, you no longer have to guess about your indoor air quality. For under $50, you can measure humidity, CO₂, and particulates. With more advanced tools, you can monitor VOCs and formaldehyde.
The key takeaways:
Your home is always in flux. Air quality can change hourly depending on the weather, activities, and outside conditions.
Continuous monitoring matters. To truly understand your home, you may need to track air quality for an entire year.
Some pollutants (like CO) can be immediately deadly. Others (like VOCs, PM2.5, or CO₂) cause long-term harm.
How much is acceptable? Personally, I want zero CO, zero VOCs, zero PM2.5—if I can make it happen.
Because when it comes to the air you breathe every minute of every day, “good enough” isn’t good enough.
Disclaimer: I don’t earn any money from the products listed above. They are simply examples of tools you can use to measure indoor air quality. Some I’ve tried personally, others I haven’t. Listing them here should not be considered an endorsement. Please make purchase and usage decisions at your own discretion and risk.
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