Hay fever is an allergic reaction to airborne substances like pollen, dust mites, or pet dander. Despite its name, it has nothing to do with hay and doesn’t cause a fever. The medical term is allergic rhinitis, and it affects roughly one in four American adults. When your immune system mistakes a harmless substance like pollen for a threat, it launches a defensive response that produces the sneezing, congestion, and itchy eyes most people associate with allergy season.
How Your Body Creates the Reaction
Hay fever starts with a case of mistaken identity. The first time you encounter an allergen like grass pollen, your immune system may flag it as dangerous. It produces a specific type of antibody called IgE, which attaches to immune cells throughout your body and essentially arms them for the next encounter.
The next time that pollen enters your nose, those armed cells recognize it immediately. They release a flood of chemicals, most notably histamine, into the surrounding tissue. Histamine is the reason your nose runs, your eyes water, and your throat itches. It dilates blood vessels, increases mucus production, and triggers inflammation in the lining of your nasal passages. A second wave of immune cells then moves into the nasal tissue, causing prolonged swelling and congestion that can linger for hours after the initial exposure.
This is why hay fever tends to get worse over time rather than better. Each exposure reinforces your immune system’s conviction that the allergen is dangerous, potentially making subsequent reactions stronger.
Common Symptoms
The hallmark symptoms of hay fever are sneezing, a runny or stuffy nose, and itchy or watery eyes. But the effects can reach well beyond your nose. Many people experience headaches from sinus pressure, a chronic cough or wheezing, and shortness of breath. The congestion can interfere with sleep, leaving you fatigued and foggy during the day.
These symptoms overlap significantly with those of a common cold, which is why many people don’t realize they have allergies. Two key differences help tell them apart: hay fever never causes a true fever, while colds sometimes do. And a cold typically resolves within 3 to 10 days, while hay fever symptoms persist for weeks or even months as long as you’re exposed to the trigger.
What Triggers It
Hay fever triggers fall into two broad categories: seasonal and year-round. Seasonal triggers follow a predictable calendar. Tree pollen dominates in early spring, grass pollen peaks in late spring and summer, and ragweed pollen takes over in fall. If your symptoms appear and disappear on a yearly schedule, one of these is likely the cause.
Year-round (perennial) triggers include dust mites, cockroach droppings, pet dander, and indoor mold spores. Pet dander can be bothersome at any time of year but often worsens in winter when homes are sealed up and air circulation drops. Mold spores blur the line between seasonal and perennial since outdoor mold peaks in warm, damp months while indoor mold persists year-round wherever moisture collects.
Understanding Pollen Counts
Local weather services and allergy apps report daily pollen counts measured in grains per cubic meter of air. The scales differ by pollen type. For grass pollen, anything under 5 is considered low. At 20 or above, most people with grass sensitivity will notice symptoms. Above 200, nearly everyone with any sensitivity is affected, and severely allergic individuals may experience intense symptoms.
Tree pollen uses a different scale entirely. Low is below 15, moderate runs from 15 to 89, and the high range stretches from 90 to 1,499. Counts above 1,500 are classified as very high. These differences matter because a pollen count of 30 means something very different depending on whether it’s measuring grass or trees.
As a general rule, low counts only bother people with extreme sensitivity. Moderate counts affect many allergy sufferers. High and very high counts impact nearly everyone who has any degree of sensitivity to that pollen type.
Who Gets Hay Fever
About 25.2% of U.S. adults reported a diagnosed seasonal allergy in 2024, according to CDC data. Women are more likely to be affected (29.5%) than men (20.7%). Prevalence peaks among adults aged 45 to 64 at 27.7%, then gradually declines in older age groups, dropping to 21.7% in those 75 and older.
Geography plays a role too. Adults in rural areas report higher rates of seasonal allergies (28.1%) compared to those in metropolitan areas (24.8%), likely because of greater exposure to grasses, trees, and agricultural pollen sources.
How It’s Diagnosed
If your symptoms follow a seasonal pattern, your doctor may diagnose hay fever based on your history alone. When the specific trigger needs to be identified, two main tests are used.
A skin prick test involves placing small droplets of common allergens on your forearm or back, then lightly scratching the skin so the liquid enters. If you’re allergic, you’ll develop a small red bump at that spot within about 15 minutes. It’s quick and gives results on the spot. A blood test measures the level of IgE antibodies your body produces in response to specific allergens. It takes longer to get results but is useful when skin testing isn’t practical.
Treatment Options
Most people manage hay fever with one or more types of medication, many of which are available without a prescription.
- Antihistamines block the histamine your immune cells release, reducing sneezing, itching, and runny nose. They come in pill, liquid, and nasal spray forms. Newer non-sedating versions are less likely to make you drowsy than older formulas.
- Nasal corticosteroid sprays reduce inflammation inside the nose and are considered one of the most effective treatments for congestion. They’re typically used once or twice daily and work best when used consistently rather than only on bad days.
- Decongestants shrink swollen nasal tissue to relieve stuffiness. They’re available as pills and nasal sprays, though nasal spray decongestants shouldn’t be used for more than a few days at a time because they can cause rebound congestion.
For people whose symptoms don’t respond well to these medications, immunotherapy offers a longer-term solution. This treatment gradually retrains your immune system to tolerate the allergen. It’s available as regular allergy shots or as daily tablets that dissolve under the tongue. Both forms require three to five years of consistent treatment to build lasting immunity, but they can significantly dial down the immune response to allergens like dust mites, grass, ragweed, tree pollen, and cat dander.
Reducing Exposure at Home
Medications treat symptoms, but reducing your contact with allergens can prevent them from starting. Running an air purifier with a HEPA filter in your bedroom captures airborne pollen and dander particles before you breathe them in. Dust and vacuum frequently, and wash bedding weekly to keep dust mite populations low. Leaving shoes at the door prevents you from tracking pollen through the house.
If indoor mold is a concern, fix water leaks immediately and run a dehumidifier in damp areas like basements. Dust ceiling fans before turning them on for the season, since they accumulate mold spores and allergens while sitting idle. On high pollen days, keeping windows closed and showering after time outdoors can make a noticeable difference in how you feel by evening.