Seasonal allergies are an immune system overreaction to airborne pollen from trees, grasses, and weeds. About one in four U.S. adults (25.2%) has been diagnosed with a seasonal allergy, making it one of the most common chronic conditions in the country. Women are affected more often than men (29.5% vs. 20.7%), and prevalence peaks between ages 45 and 64.
Why Your Immune System Reacts to Pollen
Pollen is harmless. But in people with seasonal allergies, the immune system treats it like a threat. The first time you’re exposed to a pollen you’re sensitive to, your body produces a specific type of antibody called IgE. These IgE antibodies attach to mast cells, which sit in your skin, airways, and gut, essentially arming them for the next encounter.
When that same pollen shows up again, it latches onto the IgE already sitting on those mast cells. This triggers the cells to burst open within seconds, releasing a flood of chemicals. The most important one is histamine, which immediately increases blood flow and makes blood vessels leak fluid into surrounding tissue. That’s what causes the swelling, itching, sneezing, and congestion you feel. Your body also releases compounds that tighten the smooth muscle around your airways, which is why some people with allergies also wheeze or feel chest tightness.
What Triggers Allergies and When
Different plants release pollen at different times of year, so the timing of your symptoms reveals a lot about what you’re reacting to.
- Trees (February through April): Tree pollen is the first to appear each year and is responsible for most spring allergy symptoms. In warmer regions, some trees start releasing pollen as early as December or January.
- Grasses (April through early June): Grass pollen overlaps with the tail end of tree pollen season, which is why late spring can feel especially rough for people sensitive to both.
- Weeds (August through the first hard frost): Ragweed is the dominant culprit in fall. Weed pollen season ends only when sustained freezing temperatures kill off the plants.
Local pollen counts, measured in grains per cubic meter of air, tell you how intense a given day will be. For tree pollen, anything above 90 grains per cubic meter is considered high, while grass pollen hits “high” at just 20 grains. These thresholds vary by pollen type because different pollens are more or less potent. Most weather apps and allergy websites report daily counts so you can plan outdoor activities around them.
Pollen Seasons Are Getting Longer
If your allergies feel worse than they did a decade ago, you’re probably right. Warmer temperatures, fewer frost days, and higher levels of carbon dioxide in the atmosphere are all pushing pollen seasons to start earlier and last longer. Plants also produce more pollen under these conditions, and the pollen itself may be more potent. The CDC has flagged this as a growing public health concern, noting that these shifts will expose more people to higher pollen concentrations for more weeks each year.
Seasonal Allergies vs. the Common Cold
Both cause sneezing, a runny nose, and congestion, so it’s easy to confuse them. A few differences make it straightforward to tell them apart.
Seasonal allergies almost never cause a fever or a sore throat. Colds usually do. Allergies typically cause itchy, watery eyes, while colds rarely do. And the timeline is the clearest signal: a cold resolves in 3 to 10 days, while seasonal allergies persist for weeks, often as long as the triggering pollen is in the air. If your symptoms show up at the same time every year and drag on for a month or more, that pattern points strongly to allergies.
One visual clue worth knowing: allergies often cause puffy eyelids and dark circles under the eyes, sometimes called “allergic shiners.” These come from the chronic congestion of small blood vessels beneath the skin, and they’re uncommon with a simple cold.
How Seasonal Allergies Are Diagnosed
If over-the-counter remedies aren’t cutting it or you’re unsure what you’re reacting to, allergy testing can identify your specific triggers.
The most common method is a skin prick test. Small drops of liquid containing different allergens are placed on your forearm, then a tiny needle presses each one into the skin. If you’re allergic, a small raised bump appears at that spot within 15 to 20 minutes. For airborne allergens like pollen and dust mites, this test is accurate 70 to 97% of the time.
A blood test is the alternative. It measures the levels of allergen-specific IgE antibodies circulating in your blood. This option is typically used when skin testing isn’t practical, for instance, if you have widespread eczema that would interfere with reading the results, or if you can’t stop taking antihistamines beforehand (which would suppress the skin reaction). Blood tests tend to be slightly less precise for some allergens but are highly specific for dust mites and animal dander.
Managing Symptoms Day to Day
The first line of defense is reducing your exposure. Keeping windows closed during high-pollen days, showering after spending time outside, and running air conditioning with a clean filter all help keep pollen out of your living space. Pollen counts tend to peak in the early morning, so shifting outdoor exercise to the evening can make a noticeable difference.
Over-the-counter antihistamines work by blocking the histamine your mast cells release, which reduces sneezing, itching, and runny nose. Nasal steroid sprays target the inflammation directly in your nasal passages and are generally the most effective single treatment for congestion. Both work best when you start them before symptoms ramp up, ideally a week or two before your typical season begins, rather than waiting until you’re already miserable.
Immunotherapy for Lasting Relief
For people whose allergies are severe or poorly controlled with medication, immunotherapy is the only treatment that can change the underlying immune response rather than just suppressing symptoms. It works by gradually exposing you to increasing amounts of your allergen, training your immune system to tolerate it over time.
There are two forms. The traditional approach involves regular injections at a doctor’s office, typically weekly at first and then monthly, over a period of three to five years. The newer option is a tablet or liquid placed under the tongue daily at home. Both produce similar improvements in symptom and medication scores. The under-the-tongue form causes significantly fewer side effects, though treatment courses of two years or longer may be needed for the best results. Most people who complete a full course experience lasting improvement that persists even after they stop treatment.