Allergies and Air Quality: Pollen, the AQI and Indoor Triggers

Seasonal allergies come from pollen, which the daily AQI doesn't measure, while indoor allergens like dust mites, mold and pet dander are a separate problem. Here is what NIH and the EPA say about each, and what an air purifier can realistically do.

Written from 5 public-health sources (EPA, AirNow, American Lung Association, NIH) · sources checked 2026-10-01 · see sources

Pollen and seasonal allergies

The National Institute of Environmental Health Sciences (NIH) says pollen comes from trees in the spring, grasses in the summer and weeds in the fall. Pollen in the air can trigger sneezing, congestion, watery eyes and other cold-like symptoms. Seasonal allergies, also called allergic rhinitis or hay fever, may affect nearly one in six Americans.^[2]

NIEHS also reports that weather matters: extreme weather events such as heat waves and thunderstorms have been associated with outbreaks of allergic asthma, especially in people with pollen allergy.^[2]

Pollen seasons are getting longer

NIEHS-funded research on pollen in the U.S. found:^[2]

The annual average of daily airborne pollen increased 46% between 1994–2000 and 2001–2010.
The pollen season lengthened by as much as 13 to 27 days in the northern United States between 1995 and 2009.
Higher pollen counts are related to more allergy and asthma symptoms, measured by over-the-counter allergy medication use and emergency-department and doctor visits for allergic disease.

Why the AQI doesn't show pollen

The EPA sets the AQI for five pollutants regulated under the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide.^[1] Pollen isn't one of them, so a green AQI day can still be a bad allergy day. Check a pollen forecast as well as the AQI.

The two can add up. The EPA says outdoor pollutants and pollen can aggravate the lungs, causing symptoms such as coughing, sneezing, shortness of breath, throat irritation and watery eyes, and may worsen chronic respiratory diseases such as asthma.^[3] Ozone in particular irritates the airways and can aggravate asthma.^[5]

Indoor allergens the EPA flags

Dust mites. Every home has them. They are found in mattresses, pillows, carpets, upholstered furniture, bedcovers, clothes and stuffed toys.^[3]
Mold. Mold spores float through indoor and outdoor air and can start growing when they land on damp places indoors.^[3]
Pets. Proteins in a pet's skin flakes, urine, saliva and hair can trigger reactions in people allergic to animal dander. The EPA says keeping animals out of the home is the most effective control.^[3]

Can an air purifier help with allergies?

The EPA's answer is "possibly." Multiple studies with portable HEPA air cleaners have found improvements in one or more allergy or asthma symptoms, but the improvements are not always major and don't cover every symptom.^[4]If you buy one, the EPA recommends:^[4]

Choosing a clean air delivery rate (CADR) large enough for the room. The air purifier size calculator can help.
Replacing filters regularly, because a dirty, overloaded filter won't work well.
Avoiding air cleaners that intentionally produce ozone, which is a lung irritant.

An air cleaner won't fix a mold or moisture problem.^[4] Find and fix the source first; see our mold guide.

Treatment

NIEHS notes that FDA-approved allergy treatments are available for children and adults, and that common antihistamines and nasal steroid sprays can reduce hay fever symptoms.^[2] Ask a doctor or pharmacist which option, if any, is right for you, especially for children, during pregnancy, or if you also have asthma.

What the AQI colors mean

AirNow reports the Air Quality Index (AQI) for five pollutants regulated under the Clean Air Act: ground-level ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide and nitrogen dioxide.^[1]

Green, 0–50 (Good): air pollution poses little or no risk.^[1]
Yellow, 51–100 (Moderate): acceptable, but there may be a risk for people who are unusually sensitive to air pollution.^[1]
Orange, 101–150 (Unhealthy for Sensitive Groups): members of sensitive groups may experience health effects; the general public is less likely to be affected.^[1]
Red, 151–200 (Unhealthy) and above: some members of the general public may experience health effects, and sensitive groups may experience more serious effects.^[1]

Check today's reading for your area on the city air quality pages or at AirNow.gov.

Allergies and Air Quality