Seasonal allergies cause sneezing, a runny or stuffy nose, and itchy, watery eyes. About 25% of U.S. adults have a diagnosed seasonal allergy, making it one of the most common chronic conditions in the country. While those hallmark symptoms are well known, seasonal allergies can also cause fatigue, trouble concentrating, and physical changes you might not immediately connect to pollen.
The Core Symptoms
The symptoms most people recognize as seasonal allergies center on the nose and eyes. Nasal congestion, repeated sneezing, and a clear, runny nose are the classic trio. Your throat and the roof of your mouth may feel itchy, and you might notice a persistent tickle in your nose that no amount of rubbing relieves.
Eye symptoms are equally common. Red, watery, itchy eyes are a defining feature of seasonal allergies and one of the clearest ways to distinguish them from a cold. A cold can cause watery eyes, but the intense itching that makes you want to rub your eyes constantly points strongly toward an allergic reaction.
Why These Symptoms Happen
When pollen lands on the lining of your nose or eyes, your immune system can overreact. If you’re allergic, your body has already produced a specific antibody (IgE) that sits on the surface of immune cells called mast cells. When pollen binds to that antibody, those mast cells release a flood of chemicals, most notably histamine. Histamine is what makes blood vessels swell, mucus production spike, and nerve endings fire off itch signals. Some of these chemicals release almost instantly, which is why you can start sneezing within minutes of walking outside. Others build up more slowly, fueling the congestion and inflammation that can drag on for hours.
Fatigue, Brain Fog, and Other Overlooked Symptoms
Many people with seasonal allergies feel exhausted and mentally sluggish, even when their sneezing isn’t severe. There are two reasons for this. First, nasal congestion disrupts sleep. Breathing through your mouth, waking up repeatedly, and postnasal drip all reduce sleep quality. Second, the inflammatory response itself drains energy. Your body is actively fighting what it perceives as a threat, and that immune effort leaves less fuel for everything else, including concentration and focus.
This combination of poor sleep and systemic inflammation creates what many people describe as “brain fog,” a feeling of being slow, unfocused, or unable to think clearly. If you notice that you feel mentally dull every spring or fall but can’t pinpoint why, your allergies may be the cause.
Physical Signs You Can See
Seasonal allergies can leave visible marks, especially if symptoms persist for weeks. Dark circles under the eyes, sometimes called “allergic shiners,” are blue-gray or purplish discolorations caused by blood pooling beneath the lower eyelid. Chronic nasal congestion slows blood flow in that area, and the darker the circles, the more severe or long-lasting the congestion tends to be.
Some people, especially children, develop extra creases or folds in the skin just below their lower eyelashes. These are thought to result from swelling and the constant muscle tension around the eyes that comes with ongoing congestion. You might also notice a horizontal line across the bridge of the nose from repeatedly pushing upward on the tip of the nose to relieve itching.
When Symptoms Appear by Season
Your symptoms follow the pollen calendar, and knowing which plants are active can help you identify your specific triggers.
- February through April: Tree pollen is the first to appear each year and is responsible for most spring allergy symptoms. In warmer regions, tree pollen can start as early as December or January.
- April through early June: Grass pollen overlaps with the tail end of tree season, which is why late spring can be especially rough for people sensitive to both.
- August through the first hard frost: Weed pollen dominates the fall. Ragweed is the most common culprit, but sagebrush, pigweed, tumbleweed, and lamb’s-quarters also contribute.
If your symptoms appear at roughly the same time each year and last for weeks, the pollen calendar is your best clue to figuring out what you’re reacting to.
Allergies vs. a Cold or the Flu
The overlap between allergy symptoms and a common cold confuses a lot of people. A few key differences make the distinction straightforward.
Allergies never cause a fever. If you have a temperature, you’re dealing with an infection, not pollen. Colds rarely cause fever either, but the flu usually does, and COVID-19 sometimes does. Itchy eyes strongly suggest allergies. Colds and flu don’t typically make your eyes itch. Duration is another reliable signal: a cold clears up within 3 to 10 days, while seasonal allergies can persist for weeks as long as pollen counts remain high. And allergy symptoms tend to appear almost immediately after exposure, whereas cold symptoms take 1 to 3 days to develop after you catch the virus.
Mucus color offers one more clue. Allergies produce thin, clear, watery discharge. If your nasal mucus turns thick and yellow or green after several days, that points more toward a cold or a secondary infection.
When Allergies Lead to Bigger Problems
Left unmanaged, chronic nasal congestion can set the stage for sinus infections. When swelling narrows or blocks the drainage pathways in your sinuses, mucus gets trapped. Oxygen levels inside those cavities drop, creating an environment where bacteria thrive. The result is sinusitis, which adds facial pressure, pain, and thick discolored mucus on top of your existing allergy symptoms.
Seasonal allergies can also worsen asthma. Allergic inflammation in the nose is closely connected to inflammation in the lower airways. People with both conditions may notice more coughing, wheezing, and shortness of breath during peak pollen season. Managing nasal symptoms early, before congestion becomes severe, is one of the most effective ways to reduce the risk of both sinus infections and asthma flares.