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All About Ragweed: Signs, Symptoms and Avoidance

All About Ragweed: Signs, Symptoms and Avoidance

It’s the super-villain of allergy plants, able to marshal millions of pollen grains and spread misery far and wide. But never fear! Allergic Living has the scoop on how to stop its dastardly effects. This story was first published in Allergic Living magazine.

It’s often a hot, dry late summer’s evening spent relaxing out on a porch when the first telltale signs appear. An itchy, runny nose, irritated eyes, and a tingling mouth could indicate that you’re allergic to ragweed – one of the hardiest plants and most prolific pollen producers out there.

Often sprouting up on roadsides, in vacant lots, or anywhere with uneven ground, ragweed is a major culprit for fall allergy symptoms. In 2009, the U.S. National Health survey found that 16 percent of Americans – about 49 million people – are sensitive to ragweed pollen. While its appearance is unremarkable, ragweed has special attributes that make it a formidable allergy foe.

Signs of Allergy

Although most of us think of spring as pollen allergy season, approximately 45 percent of people with hay fever and asthma show signs of sensitivity to ragweed pollen. Depending on where you live – by mid-August in the north, and as late as October in the south – ragweed pollen levels peak as the days get shorter.

Noticeable symptoms are the classic itchy, runny or stuffed up nose; red, watery and itchy eyes, and maybe prickling mouth or ears, says Dr. Richard Weber, an allergist and aerobiologist at National Jewish Hospital in Denver. “You look around and a field where they took down an old house is now laying fallow and has a bunch of weeds in it. Sure enough, it’s ragweed.”

What is It?

Although there are about 17 types of ragweed in North America, two species are the most abundant.

  • Common ragweed (Ambrosia artemisiifolia) can stand anywhere from a few inches high to 6 feet tall. It grows in tall, vertical tendrils with leaves divided into many fine lobes. When it flowers, rows of characteristic off-white blooms that look like upside-down tea cups appear.
  • Giant ragweed (Ambrosia trifida) has fewer and rounder leaves than common ragweed, and they usually have three distinct lobes, but can have up to five. Dangling similar stacks of inverted flowers, these plants can tower up to 18 feet.

Unlike fussier plants, ragweed can thrive in soil low in nutrients, and is a particular pain for farmers. Agricultural researchers have reports from farmers in several states who’ve found strains of ragweed resistant to glyphosate, one of the most widely used herbicides.

Not only does ragweed seem to grow anywhere, each annual weed produces enormous amounts of pollen – usually in the millions of grains. Designed to be aerodynamic, this pollen can travel thousands of miles from a parent plant. The pollen grains are released in clumps, held together with a sticky substance called pollenkitt, Weber explains. These clumps break apart in the air, allowing the grains to be distributed far and wide.

Unfortunately for those with allergies, ragweed pollen grains are also potent, and can prompt symptoms at counts of less than one pollen grain per cubic foot. Ragweed’s florets even have a bottlebrush-like mechanism to ensure the plant pushes out every last irritating pollen grain.

What It Isn’t

Goldenrod, another tall weed, sometimes unfairly takes the blame for early autumn allergies. It has showy yellow flowers that make it far more noticeable than plain-Jane ragweed. Goldenrod grows where ragweed thrives, and flowers at the same time.

When people see a mass of bright yellow fluff collecting, they think, “Look how sick I must be getting from that plant,” says Dr. Anne Ellis, an allergist in eastern Canada, a ragweed hotspot. Goldenrod churns out a small amount of sticky pollen, designed to be carried by insects, while ragweed produces vast amounts of pollen that is carried by the wind.

Where It Thrives

Common ragweed grows in every state except Alaska. It’s even been introduced to Hawaii. Giant ragweed has been found everywhere except Alaska, Hawaii, and Nevada. Rates of ragweed allergy are highest in the Midwest and the northeast, because that’s where the plant truly thrives.

The Season

In most of North America, ragweed gets its cue to pollinate when the late summer days grow shorter. In the northern U.S. and Canada, it peaks in late August, and only frost takes down this mighty annual. In low-frost southern states, pollination can drag on into October.

Climate change is helping ragweed to endure. One telling study published in 2011 correlated weather data and pollen counts to find ragweed season had lengthened by two to four weeks over a 15-year period in northern U.S. and Canadian sites. No matter where you are, at times ragweed feels inescapable.

Weather Effects

A soggy spring is not a good omen for ragweed allergy. More moisture in spring and summer will lead to larger ragweed plants able to churn out more pollen. As with grass and tree pollen, ragweed pollen is more likely to be grounded by moisture on a wet, drizzly day, so that’s a perfect time to venture out. Watch out for hot, dry, windy days when the grains are sure to be whizzing around.

What You Can Do

  • Confirm the culprit: To verify a ragweed allergy, see an allergist who will look for a combination of a positive skin test or blood test while asking you about any allergic rhinitis or asthma symptoms. Weber says a key sign is the timing and severity of symptoms compared with local pollen counts. Since house dust mite and outdoor mold allergies can also flare at the same time of year, the allergist needs to investigate whether ragweed is truly your problem.
  • Nasal sprays: Since we all like to get outside, a good defense against allergic rhinitis is nasal corticosteroid sprays, “but you have to plan ahead,” says Weber. The sprays work best if you start using them regularly a couple of weeks before pollen season begins. “People don’t do that,” Weber says. “They wait until they’re suffering. Then, they wonder why they’re suffering.” Two of those sprays, Nasacort and Flonase, are now available over the counter in pharmacies.
  • Antihistamines: Although they won’t block the biochemical cascade set off during an allergic reaction, some people find non-sedating antihistamines are helpful to keep symptoms at bay.
  • Immunotherapy Options: Allergy shots are an option for those who are walloped by ragweed year after year. It takes about five years, and many, many needles, but evidence suggests the benefits can last a lifetime.

More convenient (but not proven as effective) is a yearly set of four shots of Pollinex-R. The treatment involves one needle a week for four weeks just before pollen season starts. People may need less allergy medication if they get the shots.

For those who cringe at the notion of needles, a recently available under-the-tongue tablet called Ragwitek may offer relief. Like allergy shots, the prescription drug works by desensitizing the immune system to ragweed pollen. To get the best protection, Ellis advises starting the tablets daily as early as April and taking them until the end of ragweed season. Research has found the sublingual tablets are nearly as effective as allergy shots, and have fewer serious side effects.


  • Taking extra steps to stop ragweed pollen from getting inside is worth the effort.
  • Keep windows closed and use an air conditioner with a HEPA filter on hot days.
  • Ragweed is a late-morning pollinator, making early morning a better time to get outside. Rain also keeps it grounded.
  • Get rid of ragweed on your own property by simply plucking the plants out at the root – preferably before pollination starts. (If you have the allergy, wear a mask).
  • After being outdoors, change clothes right away, and shower if time allows.
  • Washing (or at least brushing) pets after they’ve played outside can reduce pollen tracked indoors.
  • Use the dryer in pollen season, as hanging clothes out to dry collects allergens.

Dodging pollen in the first place to prevent reactions can be just as important as finding effective treatments. So take the time and get creative about minimizing your exposure to ragweed’s abundant pollen.

Reference: Allergic Living. (2016). All about ragweed: Signs, symptoms and avoidance. Retrieved from: