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Whether the culprit is tree pollen, grass or ragweed, seasonal allergies affect about 25 per cent of the Canadian population. But how do allergens differ from year to year, and how might our changing climate be playing a role in the severity or onset of symptoms? Schulich Medicine & Dentistry professor Dr. Samira Jeimy is an expert in clinical allergy and immunology and an allergist at the Allergy and Immunology Program at St. Joseph’s Health Care London. She spoke with Western News to help separate fact from myth.  

Western News: When do most seasonal allergies set in and why does the timing vary between people?

Dr. Samira Jeimy (SJ): Onset of seasonal allergy symptoms depends on what a person is allergic to. In Southwestern Ontario, tree pollen is usually the main spring trigger, often starting in early spring and continuing into late spring. Grass pollen tends to become more apparent in late spring and summer. Ragweed and other weed pollens usually peak later, in late summer and early fall. The timing can vary for different people because not everyone is allergic to the same pollen. One person may feel symptoms in April because of tree pollen, while another may be fine until ragweed season in August. Some people are allergic to multiple pollens. There are also year-round allergens that “fluctuate” throughout the year – mould and dust mite allergens flourish in humid weather. Weather patterns can also have an impact. For example, a warm spell can push plants to pollinate earlier. Windy days spread pollen more widely. Rain can temporarily wash pollen out of the air, although damp weather can increase mould exposure for some people.  

Does the severity of seasonal allergies change from year to year and is climate change playing a role?

SJ: Symptoms can change from year to year because pollen seasons are affected by temperature, rainfall, humidity, wind and how early plants begin growing. Climate change is part of the bigger picture for sure. Warmer temperatures and higher carbon dioxide levels can lengthen the growing season and increase pollen production. In North America, data from 1990 to 2018 showed that pollen seasons became longer and pollen concentrations increased over time, with climate change contributing to these trends. The long-term trend is toward longer and more intense pollen seasons, while individual seasons still vary.  

What effect does pollution have on the severity of symptoms?

SJ: Pollution can make allergy symptoms worse. Pollutants can irritate the lining of the nose, eyes and airways, making people more reactive to pollen. Air pollutants can also interact with pollen and may make allergic inflammation worse. This is relevant for most people with allergic rhinitis, asthma or sensitive airways. In practical terms, patients may feel worse on days when pollen is high and air quality is poor. For those with asthma, pollen plus poor air quality can be a more difficult combination than either exposure alone.  

Is this shaping up to be a particularly bad season?

SJ: As of early March, London pollen forecasts have shown high tree pollen, with oak, birch and mulberry listed among top allergens. That fits with what many spring allergy patients are feeling. For patients allergic to tree pollen, this may already feel like a difficult spring. Whether the whole season is unusually severe will depend on weather patterns, rainfall, wind and pollen levels over the coming weeks.  

What are some ways to manage symptoms?

SJ: The best approach is to treat early and consistently, rather than waiting until symptoms are severe. I have a preference for allergy testing to help people figure out their triggers. For many patients, the most effective first-line treatment is a nasal corticosteroid spray or a corticosteroid/antihistamine combo spray, used daily during the season. Technique is very important and not well taught. People should aim the spray slightly outward toward the ear, not straight up toward the middle of the nose. Non-sedating antihistamines can help sneezing, itching and runny nose. Allergy eye drops can help itchy or watery eyes. Saline rinses can help remove pollen and mucus from the nose. I also recommend some practical steps to limit exposure, including keeping windows closed when pollen is highest (between 4 and 10 a.m.), showering or rinsing hair after being outdoors, changing clothes after outdoor activity, avoiding drying laundry outside, wearing sunglasses outdoors and checking pollen counts and air quality when planning exercise. For people with persistent symptoms despite medications, allergen immunotherapy can be very helpful. Immunotherapy is different from symptom medication because it can change the immune response over time.  

What are some common myths?

SJ: One myth is that seasonal allergies are “just a nuisance.” For some people they are mild, but for others they can really affect sleep, school, work, exercise, asthma control and quality of life. Another myth is that all antihistamines are the same. Older sedating antihistamines can cause drowsiness, impaired performance and side effects. For routine allergy symptoms, newer non-sedating options are preferred. Another common myth is that nasal sprays are addictive. Steroid nasal sprays are not addictive. The sprays that can cause rebound congestion are decongestant sprays, such as oxymetazoline, if used for more than a few days. Another myth is that allergies mean the immune system is weak. Allergies are not immune deficiency. They are an overreaction of the immune system to harmless environmental proteins like pollen. A final myth is that people can always diagnose the trigger based only on the month. Timing gives clues, but isn’t perfect. Testing can help identify whether symptoms are due to tree pollen, grass, ragweed, mould, dust mite, pets or something else.  

How can we determine if symptoms are allergy related?

SJ: Not every spring nasal symptom is allergy. Viral infections, non-allergic rhinitis, irritant exposure, chronic sinus disease, medication effects and reflux can overlap with allergy symptoms. Typically, allergies cause itching, sneezing, clear runny nose, congestion and watery or itchy eyes. Fever, thick, discoloured mucous, severe facial pain or symptoms that do not track with pollen exposure may point to something else. I would also emphasize that asthma symptoms during pollen season should not be ignored. Coughing, wheezing, chest tightness or shortness of breath during allergy season may mean the lower airways are involved. Those patients should be assessed by a doctor.