Signs and symptoms of poor indoor air quality
Poor indoor air quality (IAQ) shows up two ways. In people: headaches, fatigue, dizziness, dry or irritated eyes and throat, congestion, and worsened allergy or asthma symptoms - often easing when you leave and returning when you come home. In the house: persistent dust, stale or musty odors, window condensation, off humidity, and any visible mold or past water damage.
What causes it - and the healthy targets
The most common cause is inadequate ventilation that traps pollutants indoors, followed by moisture and mold, combustion byproducts from gas appliances or an attached garage, VOCs from paints and cleaners, and outdoor infiltration like wildfire smoke and pollen. Here is what healthy indoor air looks like by the numbers:
| Measure | Healthy target |
|---|---|
| Indoor AQI | Under 50 |
| Carbon dioxide (CO2) | Below ~1,000 ppm |
| Relative humidity | 30 - 50% |
| PM2.5 particulates | As low as possible |
A consumer monitor reads these; a professional assessment adds combustion safety and duct testing.
Wildfire smoke in the foothills. When the outdoor AQI climbs above 100-150, keep windows closed, run your HVAC fan with a MERV 13 or higher filter, and add a portable air cleaner in bedrooms. Fixing IAQ starts with the source, then ventilation, then filtration.
Indoor Air Quality Questions, Answered
How can I test my indoor air quality at home?
Start with a consumer indoor air quality monitor that reads particulates (PM2.5), carbon dioxide, VOCs, and humidity, and install a carbon-monoxide detector on every level. For a full picture, a professional assessment measures those plus combustion safety and duct leakage and pinpoints the source. A phone alone cannot measure indoor air - it only reports the outdoor AQI for your area.
What are the symptoms of poor indoor air quality?
Common symptoms include headaches, fatigue, dizziness, dry or irritated eyes and throat, congestion, and worsened allergy or asthma symptoms. A telling sign is when symptoms ease after you leave the house and return when you come back, which points to something in the home rather than a general illness.
What are the signs of poor indoor air quality in a house?
In the home itself, watch for persistent dust that returns quickly, stale or musty odors, condensation on windows, high or very low humidity, and any visible mold or past water damage. Frequent dusting and rooms that always feel stuffy are practical everyday clues.
What is the most common cause of poor indoor air quality?
Inadequate ventilation is the most common cause. When a home does not exchange enough fresh air, pollutants from cooking, cleaning products, off-gassing materials, and moisture build up indoors. Other frequent sources are mold from moisture, combustion byproducts from gas appliances, and dust and dander circulated through the ducts.
Can bad indoor air quality make you sick?
Yes. In the short term poor indoor air can cause headaches, irritation, and worsened allergies or asthma, and carbon monoxide from faulty combustion can be dangerous. Long-term exposure to particulates and pollutants is linked to respiratory and cardiovascular problems, which is why source control and good filtration matter.
What is a good indoor air quality number?
Aim for an indoor air quality index (AQI) under 50, carbon dioxide below about 1,000 ppm, PM2.5 as low as possible, and relative humidity between 30 and 50 percent. Readings much above those ranges suggest ventilation, filtration, or humidity problems worth addressing.
How do I fix bad indoor air quality?
Work in this order: control the source (fix moisture, vent combustion, reduce VOCs), add ventilation or fresh air, then improve filtration with a MERV 13 or higher filter, a media air cleaner, or HEPA. Keep humidity between 30 and 50 percent and seal or clean leaky ducts. Matching the fix to the actual source beats guessing.
At what AQI should I stay indoors?
Sensitive groups should limit outdoor time once the AQI passes 100, and everyone should limit it above 150. During Sacramento-area wildfire smoke events, keep windows closed, run your HVAC fan with a high-MERV filter or a portable air cleaner, and avoid drawing in outside air until the AQI drops.
Breathe Easier at Home.
We assess your indoor air - particulates, humidity, and combustion safety - then recommend filtration, ventilation, or duct work that fixes the source, not just the symptom.