Ragweed Allergy: It’s Nothing to Sneeze At

You’ve probably heard of the term hay fever or the fancy medical synonym allergic rhinitis. In fact, you may have first-hand experience with symptoms that land in this category. If not, you definitely have that friend who does—the one who sneezes way too loudly and goes through way too many tissues. A bunch of stuff can set off allergic rhinitis, but as the fall approaches in North America, the biggest culprit is ragweed. Here is a quick overview of ragweed allergy, starting with some background and ending with a few numbers.

 

Background

Allergic rhinitis refers simply to inflammation of the nasal cavity due to an allergic reaction. Typically, such allergic reactions are to otherwise benign airborne substances, and symptoms include runny nose and sneezing. The same process can affect any part of the body exposed to the same airborne substances, explaining other symptoms such as itchy/watery eyes, itchy throat and ears, and even asthma.

To understand this type of allergy, you need to know a tiny bit about IgE, a class of antibody that is often attached to cells called mast cells. For a variety of reasons, some people make IgE to benign airborne substances (allergens), recognizing them as much more of a threat than they really are. When an IgE molecule encounters an allergen, this causes the mast cell to which the IgE is attached to release a bunch of mediators designed to fight the problem. Unfortunately, there really wasn’t a problem to begin with, and all you’re left with is the inflammation that the mediators cause. The most well-known mediator is histamine, though others such as leukotrienes are in the mix.

In some cases, the culprit allergens can be found year round. Examples include pet dander and dust mites. In other cases, the allergens are seasonal, explaining the common use of the term seasonal allergies. In many cases, seasonal allergies are caused by a reaction to the pollen of seed-bearing plants that are prominent at the time.

A pollen grain comes from the male structure of such plants and needs to be transported to the female structure for fertilization to occur. When this transport occurs by the wind, humans are at risk for allergies. (As a comparison, plants that are pollinated by insects are much less likely to cause allergies.)

 

Ragweed

Ragweed is a flowering plant that is native to the Americas, particularly North America. Multiple species exist, though the most widespread in North America is Ambrosia artemisiifolia (also called common ragweed), whose wind-dispersed pollen serves as a major cause of allergies. Its bloom period begins in late summer, explaining why it is a very common cause of fall allergies.

Ragweed can be seen next to more attractive looking plants with bright yellow flowers called goldenrods. This association leads many people to think they are allergic to goldenrods, but the insect-pollinated plants are not a contributor to seasonal allergies.

While common ragweed is native to the Americas, it has made its way across the world thanks to human activity. The seed was probably introduced to Europe in the 19th century, getting a free trip across the Atlantic Ocean by inadvertently landing in other supplies. At this point, common ragweed is found on all continents except Antarctica.

And now, a few numbers:

1 billion

The approximate number of pollen grains per season that one ragweed plant can produce. The pollen can be carried hundreds of miles by the wind and cause allergy symptoms even where the plant is not visible.

18

The average size in micrometers of a single ragweed pollen grain. (A micrometer is one-millionth of a meter.)

10

The average number of weeks the ragweed pollen season lasts, though climate change may be extending that duration. In most areas, the plant begins to pollinate around mid-August and does not stop until the first frost. Pollen counts can vary from year to year.

As a bonus fact for this number, exposure to as few as 10 pollen grains can cause allergy symptoms.

20

The approximate percent of Americans that are affected by ragweed allergy. (The severity of symptoms can vary widely.) This number explains the association of ragweed with decreased school and work productivity.

5

The estimated percent of ragweed allergy sufferers in Asia. The plant is established in Japan, South Korea, and China.

 

So go ahead and tell your buddy to sit inside with the windows closed for about 10 weeks. Okay, don’t do that. But do tell them to shower after going outside, take an antihistamine, and—if they’re really desperate—see an allergist. Trust us when we tell you, they’re not that bad.

 

Anitha Shrikhande, a board-certified allergist and esteemed family member of ComposeMD’s founder, contributed to this article.