What is ragweed allergy?

Ragweed growing on the edge of a field. The pollen is a major cause of hay fever and cross-reacts with some tree pollens too

Ragweed is a pest and so is its pollen. The plant is one of the biggest culprits behind hay fever, and not just in North America. Ragweed has invaded every continent except Antarctica and is spreading to new areas all the time. During peak season the ragweed pollen count may reach 250 grains per cubic meter (35ft3) of air. And it can take as little as 10 grains to trigger an allergic reaction.

Around 15% of people in the United States reach for their hypoallergenic tissues when ragweed starts flowering. 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.

What exactly is ragweed?

Ragweed is a cousin of the daisy and sunflower – though you wouldn’t know it. Unshowy greenish flower spikes grow from tall, bushy, branching stems. There are 17 species of ragweed plants native to North America. Two are particularly widespread: common or short ragweed (Ambrosia artemisiifolia), which grows to 3.5ft; and great or giant ragweed (Ambrosia trifida), which can reach over 13ft tall.

Where does ragweed grow?

Ragweed allergies have been a major health problem for decades. The plant has invaded every state in the US except Alaska. It has even arrived in Hawaii. But it’s most abundant in the east and Midwest. Ragweed thrives in poor soil and undisturbed ground. That’s why it likes woodland, dry fields and pastures, roadsides and vacant lots.

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.

Did you Know...?

  • 75% of people with pollen allergy are allergic to ragweed
  • The seeds can survive for 40 years in the soil so ragweed plants can still pop up when you think you’ve got rid of them
  • Ragweed is a short-day plant which means it won’t start flowering until after the longest day on 21 June, the summer solstice
  • Ragweed allergies are such a problem there’s even an #InternationalRagweedDay. It’s on the first Saturday of summer, the one after the solstice
  • Ragweed immunotherapy has been in use for over 100 years. The first successful trial of allergy shots took place in 1913.

Why does ragweed make some people sneeze?

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.

How long is ragweed season?

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 Minneapolis gained an extra 18 days. That means a longer allergy season too.

How does allergy
testing work?

A woman standing in the wind, biting down on her finger.

Ragweed allergy symptoms

Symptoms of pollen allergy tend to affect your nose and airways as you breathe in the tiny particles. Contact can cause an allergic reaction in your eyes and skin too:

  • Hay fever: a blocked or runny nose, post-nasal drip and sneezing. Also known as seasonal allergic rhinitis
  • 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

Ragweed allergy: cross reactions

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.

So how do I know if I’ve got ragweed allergies?

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.

Be pollen prepared

Do you have ragweed allergies? Get daily ragweed pollen, weather and air quality data on your phone and track your allergy symptoms with our free app.

Klarify app

8 tips for avoiding ragweed pollen

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:

  • Limit your time outdoors especially in the middle of the day when ragweed pollen reaches peak levels
  • Learn to love cooler mornings (below 50F) and rainy days as the ragweed pollen count tends to be lower  
  • Carry an allergy survival kit: a mask, wraparound sunglasses, wide-brimmed hat, hay fever meds and hypoallergenic tissues
  • Keep windows closed in ragweed pollen season. The tiny pollen grains travel long distances in the wind so they can still be in the air at night after other pollen has landed
  • Use a special air purifier to keep your home as allergen-free as possible
  • Change your clothes and outdoor shoes as soon as you get home so as not to bring pollen in with you – and do it in the bathroom
  • Shower and wash your hair after you’ve been out
  • Pets pick up ragweed pollen too so don’t let them sleep in your bedroom
Quote Image

Each ragweed plant produces up to a billion pollen grains during the season. The tiny particles can travel huge distances on the wind. Ragweed is an allergy machine.

Treatments for ragweed allergy symptoms

Eye drops and nasal salt water rinses can be soothing and help get rid of pollen. Medications to control symptoms may also make living with ragweed allergy easier. You can take some types from a couple of weeks before the pollen season to boost your defenses. You may still get allergic rhinitis and other allergy symptoms but hopefully they’ll be milder.

Antihistamines block the chemical histamine that’s triggering your hay fever. There are tablets, liquids, eye drops, nasal sprays and creams. Corticosteroid nasal sprays can help calm inflammation. And decongestants tackle that stuffy nose but you should only take them for a limited time.

Many antihistamines and other hay fever meds are available over the counter. For other options you may need a prescription. Ask your pharmacy or healthcare provider for advice.

Ragweed allergy immunotherapy

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.

Try our quick quiz to find out more about allergy immunotherapy and the different treatment options.

Share your story

If you've read all the way to the end of this article about ragweed allergy, thank you. We'd love to know what you think. Have you tried any of the tips we've suggested? Or do you have any of your own that you'd like to share with others? Head over to our Facebook page or email us and share your story.

klarify takes allergy science and makes it simple, and we have rigorous process for doing this. We use up-to-date and authoritative sources of information. Medical experts review our content before we share it with you. They and the klarify editorial team strive to be accurate, thorough, clear and objective at all times. Our editorial policy explains exactly how we do this.