Will the real allergen please stand up?

Thursday August 23, 2012

‘Tis the season for sneezing, runny nose, itchy and watery eyes, and sometimes a scratchy throat -- even asthma attacks. It's also the season, now through frost, for two especially common plants: inoffensive Canada goldenrod (Salidago canadensis), with its brilliant yellow flower plumes, and the easily overlooked common ragweed (Ambrosia artemisiifolia) -- the real culprit.

The unremarkable ragweed often grows a couple of feet and occasionally as much as 5 feet tall. It blends well in gardens, along fencerows and roads, in vacant lots, in playgrounds, and even in cultivated fields and along beaches. Its long, thin, cone-like green flowers are no match for the more obvious Canada goldenrod that shouts with eye-catching color, easily growing 5 feet tall or higher in fields and along roadsides.

Nearly 25 goldenrod species grow in the Berkshires, and some may be diminutive, as short as 1 foot high. Regardless of size or season, the goldenrods are pollinated by insects; goldenrods produce a heavy, sticky pollen that cannot become airborne, so they do not cause seasonal allergy symptoms.

Local allergist Dr. Thomas B. Edwards of Berkshire Allergy Care said that of his patients, some 60 percent are allergic to one or more plants, while 45 percent are allergic to ragweed. Mike Tringale, the vice president of external affairs at the Asthma and Allergy Foun dation of America, said those figures were consistent with statistics nationwide. Ragweed allergy is among the most common, he said.

Like other allergies, reaction to ragweed pollen occurs when our body's immune system mounts a strong reaction or response to a foreign (often harmless) substance -- in this case, miniscule pollen grains released into the air by mature ragweed flowers.

Our immune system reacts to the pollen as if it were an actual threat, and immune cells start making antibodies and flooding the bloodstream with histamine, a compound causing an assortment of bothersome to irritating allergy symptoms. Anti histamines work by blocking the action of histamine receptors in the body, which prevents the immune-system reactions that cause allergy symptoms.

Other plants are also prolific pollen producers, among them lambs quarters, pigweed, plantain and sheep sorrel. While these may cause allergies in some people, common ragweed and giant ragweed account for more seasonal allergies than all other pollen sources combined.

Why? The thousands of tiny male flowers on an average ragweed plant result in production and release about 1 billion pol len grains most often re leased in mid morning as dew .

Those allergic may try staying inside with windows closed, investigate antihistamines and immunotherapy, bathe outdoor pets frequently to reduce pollen they bring inside, and shower before bed to reduce transferring pollen into bed and in creasing nighttime exposure.

According to a report in Scientific American, approximately ragweed affects 22 million people in the United States who have seasonal allergies.

Miriam Rotkin-Ellman, a public health scientist at the Natural Resources Defense Council said, "There is a growing body of science showing warming temperatures and carbon dioxide levels cause increases in pollen from ragweed."

Readers experiencing ragweed-instigated allergies, and even those who are not, may ask, "What good is it anyway?"

It's a native plant, and so it isn't surprising that it offers wildlife food and cover. Rag weed seeds persist on plants into the winter, providing a source of energy for various sparrows, pheasants, quail and mourning doves. During the growing season, various butterfly and moth larvae feed on its leaves.

That may not be enough to reconcile allergy sufferers to its existence, though.

  • The pollen from goldenrod cannot become airborne and therefore does not cause seasonal allergy symptoms.
  • Ragweed (common and giant) causes more seasonal allergies than any other pollen source.
  • The flowers on a ragweed plant release 1 billion pollen grains into the air, mainly in the early morning.
  • According to Dr. Thomas B. Edwards of Berkshire Allergy Care, 60 percent of his patients are allergic to one or more plants, and 45 percent are allergic to ragweed.
  • Scientific America: "About 22 million people in the United States who have seasonal allergies are affected by ragweed."


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