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revised April 01, 2020

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Environmental Allergies

Allergies, also known as allergic rhinitis or hay fever, occur when your immune system overreacts to particles in the air that you breathe. Your body's defence system (immune system) attacks the particles in your body, causing symptoms, such as sneezing and a runny nose. The particles are called "allergens" because they can cause an allergic reaction.

Note: This web page is for information purposes only. It is NOT a substitute for professional medical advice.

What causes allergies?

Many environmental allergies are caused by pollen from:

  • trees
  • grasses
  • weeds

Environmental allergies can also be caused by:

    Environmental allergies
  • dust mites
  • animal dander
  • cockroaches
  • mould
  • workplace conditions
    • cereal grain
    • wood dust
    • chemicals
    • animals

The types of pollen that most commonly cause allergic reactions are produced by plants (trees, grasses and weeds) that do not have large flowers. These plants create small, light, dry pollen granules that can travel long distances through the air. Most allergenic pollen comes from plants that produce it in huge quantities. For example, a single ragweed plant can generate a million grains of pollen a day.

The chemical makeup of pollen is the basic factor that determines whether it is likely to cause hay fever. For example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing allergy. However, because pine pollen is heavy and tends to fall straight down rarely reaching human noses, it appears to cause fewer allergies than other types of pollens.

The release of pollen takes place seasonally:

  • Tree pollen is released in early spring.
  • Grass pollen is released in early June.
  • Ragweed pollen is released in August and early September.
  • Mould from leaf litter occurs in the fall.
A young ragweed plant

What are common plant allergens?

Ragweed is the most common cause of seasonal allergies. It's estimated that 75 per cent of people with hay fever are bothered by ragweed.

Among North American plants, weeds are the most prolific producers of allergenic pollen. Grasses and trees are also important sources of allergenic pollens. You can identify common weeds and grasses found in Ontario by visiting ontarioweeds.com.

Male flower with pollen clusters

Dandelions shed airborne pollen, but cause limited allergies because the pollen is heavy and tends to fall straight down rarely reaching human noses. The floating fluff is actually the seed, not the pollen, and does not cause allergies.

What are the symptoms?

In most cases, when you have allergies you may experience some of these symptoms:

  • sneezing
  • itchy and watery eyes
  • coughing
  • wheezing
  • a scratchy, irritated throat
  • headaches
  • difficulty sleeping

Coughing and wheezing may be worse in people with asthma and Chronic Obstructive Pulmonary Disease (COPD).

How do I find out if I have allergies?

To find out if you have allergies, talk to your doctor about your symptoms, when you get them and what makes them worse or better.

If you have severe symptoms, you may need to have allergy tests to find out what you are allergic to.

Your doctor may do a skin test. In this test your doctor puts a small amount of an allergen into your skin to see if it causes an allergic reaction.

How can I treat my allergies?

Unless you have other health problems, such as asthma, you may take over-the-counter medicine to treat your symptoms at home. If you have other health problems, talk to your doctor first. Older adults, children and women who are pregnant or breastfeeding should also talk to their doctor before taking medication.

If home treatments do not help or the over-the-counter medicines make you sleepy or cause other side-effects, then your doctor can prescribe medication. If your allergies continue to bother you and you cannot avoid the things you are allergic to, you and your doctor can decide if you should get allergy shots (immunotherapy) to help control your symptoms. For allergy shots to work, you may need to do skin or lab tests first.

How do I prevent allergic reactions?

  • Stay inside when pollen counts are high (mid-day to late afternoon). Pollen counts are generally lowest just after sunrise.
  • Watch local weather reports or visit the Weather Network for local pollen counts.
  • Keep windows closed and use air conditioning at home and in the car to reduce exposure to outdoor pollens. If a window-type air conditioner is used, keep the vent closed.
  • Do not use a fan with an open window, as this can bring more pollen into your home.
  • Mow your grass often. If possible, have a family member or friend do it for you. If this is not possible, wear a dust/pollen mask while you mow.
  • Take your holiday during the peak of the pollen season in a place where the plants you are allergic to don't grow.
  • Wear wrap-around sunglasses to prevent pollen from blowing into your eyes.
  • Avoid places with lots of weeds and tall grasses, like parks or fields.
  • Ask your doctor about anti-histamine medications and prescription nose and eye drops to relieve symptoms. Be careful when driving or using machinery as some allergy medicines can make you sleepy.
  • Clean your furnace/air-conditioner filter frequently to remove pollen.

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Revised: April 01, 2020

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