Do you get hay fever symptoms like a blocked or runny nose that drag on for weeks in late summer? Are these symptoms interfering with work or studying or stuff you love doing? Ragweed allergy can have quite an impact on your life. So let’s find out more about this troublesome plant and what to do if you think you might be allergic to it.

Ragweed is a cousin of the daisy and sunflower – though you wouldn’t know it. There are three species in Canada. The most widespread is common or short ragweed (Ambrosia artemisiifolia), an upright hairy stemmed plant growing up to 3.6 feet tall. The leaves are usually deeply divided and dark green. Unshowy greenish flowers with yellow stamens cluster around the stalk in a spike.

Ragweed pollen traces have been found from 60,000 years ago in Canada. It grows in cultivated fields, gardens and vacant lots. Roadsides are a favourite spot. So too are fence lines and sidewalk edges. Ragweed is a particular problem in southern Ontario and Québec.

Ragweed plants produce up to a billion pollen grains during the season. The tiny particles travel huge distances in the wind; they’ve even been found 400 miles out to sea. So you don’t have to live near ragweed to get ragweed allergy symptoms. It’s an allergy machine.

Allergies start in the immune system. It’s your immune system which protects your body against bacteria and viruses and other threats. Sometimes it makes a mistake and overreacts to a harmless substance like ragweed pollen. Your immune system does all it can to get rid of the tiny particles from your body. It produces antibodies called Immunoglobulin E (IgE). They tell other cells to release chemicals including histamine. That’s what causes those annoying ragweed allergy symptoms.

Ragweed plants start flowering in July or August and go on for 6 to 10 weeks. In many areas the release of pollen peaks in mid-September. Exactly when symptoms of ragweed allergies may strike will depend on where you live and the weather that year. You could still have a runny nose in October or even November if it’s still warm and dry.

Ragweed pollen only stops causing trouble once the first frost kills the plants. That’s happening later and later in the year because of rising temperatures due to climate change. A study of 11 places across the US and Canada found that 10 of them had a longer ragweed pollen season in 2015 compared to 20 years earlier. For instance Winnipeg gained an extra 25 days and Saskatoon 24. That means a longer allergy season too.

Ragweed plants start flowering in July or August and go on for 6 to 10 weeks. In many areas the release of pollen peaks in mid-September. Exactly when symptoms of ragweed allergies may strike will depend on where you live and the weather that year. You could still have a runny nose in October or even November if it’s still warm and dry.

Ragweed pollen only stops causing trouble once the first frost kills the plants. That’s happening later and later in the year because of rising temperatures due to climate change.

• Eye irritation: inside your eyelids and on the surface of the eyes making them itchy, burning, red and watery
• Lower respiratory symptoms: a cough, shortness of breath, tight chest and wheezing
• Ragweed rash: itchy red streaks behind the ears or on the face and eyelids, the V of neck and forearms. Also known as airborne contact dermatitis

If you have an allergy to ragweed pollen you might react to other members of the daisy family (Asteraceae) too. As well as sunflowers, that includes cocklebur, marsh elder and mugwort. Chamomile, the groundsel bush and rabbit brush may cause symptoms too.

Cross-reactions happen because the other pollen contains a protein similar to the allergens in ragweed pollen. That’s also why some people get a mild, local reaction in their mouth, throat, lips or face when they eat certain foods. It’s called pollen food syndrome or oral allergy syndrome (OAS). Sunflower seeds, cantaloupes, honeydew melons, watermelon, banana, cucumber, white potato and zucchini all contain a similar protein to ragweed pollen. So they could make your mouth tingle if you’re allergic to ragweed.

The allergy symptoms may sound familiar. The timing might be right too. But there are other weed pollen allergies that strike in late summer and early fall. And cross-reactions can cause confusion too. So you’ll need to talk to your health care provider to be sure. They’ll want to know your medical history and whether allergy runs in the family. And they’re likely to suggest a skin prick test or allergy blood test before making a diagnosis.

If it is ragweed allergy, you can start taking practical steps to limit exposure to your trigger. Your healthcare provider or allergist will also discuss the treatment options with you.

Pollen counts and calendars are useful tools to warn you when it might be better to stay indoors. You can even get up-to-date information about pollen levels on your phone. And here are some other ways to help keep contact with ragweed pollen to a minimum:

Your doctor may suggest immunotherapy. It depends on the nature and severity of your allergy. There are two types of ragweed immunotherapy: allergy shots and tablets that dissolve under your tongue. Both act on the root cause of your ragweed allergy rather than just the symptoms. This is the only allergy treatment that can change the course of your disease.

Controlled, repeated exposure to the allergen reprograms your immune system so it doesn’t see ragweed pollen as a threat anymore. A course of allergy immunotherapy takes about three to five years. But it can stop or greatly reduce your allergy symptoms and bring long-term relief.