The Ohio River basin is great at collecting dust, pollen and mold, an unfortunate tendency for many of the region's residents.

Location, location, location. When it comes to allergies, Ohio really is the heart of it all.

The Ohio Valley has the dubious distinction of being home to two cities repeatedly ranked among the most challenging places in the country to live with seasonal allergies.

Those two cities —Dayton and Louisville, Ky.—rank near the top of the nation’s “allergy capitals,” according to the Asthma and Allergy Foundation’s twice-yearly reports. The cities are named specifically because they each house one of the National Allergy Bureau’s official pollen counters.

Besides pollen and mold counts, the foundation’s report examines allergy medication usage and availability of board-certified allergists.

Why Ohio? Thank climate, ideal growing conditions and geography, experts say. And don’t forget mobility. Pollen can travel hundreds of miles, and the Ohio Valley’s terrain provides a comfortable resting place for pollen that’s made a long journey from the west, says Alan Reppert, senior meteorologist with AccuWeather in State College, Pa. The mountains of West Virginia can slow the flow in some cases, Reppert says.

But wait, you think: I live in Columbus, not in a valley. Unfortunately for those with allergies, the Ohio River corridor has a much larger sphere of influence than its immediate surroundings.

The term “Ohio Valley” tends to be more a regional definition than a strictly geographical one, says NBC4 meteorologist Ben Gelber. While the valley itself is only a few miles wide, the region includes sections of the Buckeye state, Indiana and Kentucky, as well as extreme northwestern West Virginia and southwestern Pennsylvania. Its southernmost border is at the junction of the Ohio and Mississippi rivers in Cairo, Ill.

For forecasting purposes, meteorologists sometimes refer to sections of the Ohio River Valley as upper, middle and lower. Columbus is in the upper region. Weather systems tend to follow the Ohio River Valley, making them a preferred storm track, Gelber says. The region also could be the path of least resistance where winds can channel into a more homogeneous, low area.

Warmth, moisture and the region’s tendency to be at the receiving end of pollen transportation make it ideal for the pollen population. The broad, fertile valley with its lush vegetation also is a productive breeding ground for native pollen. “It’s just our luck,” Gelber says.

Ragweed and mold are prolific in the Ohio Valley, Gelber says, and with recent weather trends, that only is increasing. “If you have ragweed allergies, you’re in for it.”

While the term “climate change” can provoke disagreement, meteorologists and allergy specialists agree that changes in weather patterns have a direct effect on the amount and duration of seasons when pollen is present and active.

Gelber notes that average annual temperatures and precipitation have risen in recent decades. Our region also receives more winds from the southwest than it did several decades ago.

That results in longer frost-free seasons, meaning earlier starts to spring pollen season and later ends to fall, with greater overlap between the two. “Last year we had a double whammy with peak seasons, and this looks like it will be another banner year,” Gelber says. “As wet as we’ve been with nearly double average precipitation, one has to think pollen and mold spores will be abundant.”

Nasal allergies affect more than 50 million Americans. The American College of Allergy, Asthma and Immunology reports that plant-based respiratory allergies are on the rise, with as many as 30 percent of adults and 40 percent of children having at least one allergy.

Dr. Princess Ogbogu, director of the allergy/immunology division at Ohio State University’s Wexner Medical Center, has seen the effect. “We consistently have tended to have pollen changes due to changes in the weather pattern,” she says.

In a phenomenon known as super pollination, real winter is starting later and ending earlier. “It may be hard to believe with this year’s polar vortex, but we now are experiencing more temperate conditions,” Ogbogu says. For example, a good ground freeze is needed to knock ragweed out of commission, and that is occurring later now, she says. At the same time, more extreme heat in the summer provides excellent growing conditions for plants that produce large amounts of pollen.

Regardless of what causes it, a longer pollen season means more time for those with allergies to become sensitized to allergen antibodies and produce a response in the form of sneezing, coughing, itchy eyes, runny noses and other misery-making symptoms.

Heard enough? Ready to move to Arizona? It could work, but maybe not long-term, experts say. Since allergies are an abnormal immune response, people who have allergies in Ohio likely are already more acutely sensitized to allergens as a whole. That means the body’s immune system is already vigilant and can develop allergic immune responses in its new environment. 
Someone who moves to escape ragweed may also develop allergies to plants native to another region.

Says Ogbogu, “I’ve seen cases where people’s allergies have subsided for a few years after moving, but then they become activated again.”

Even if you choose to remain in an allergy hot spot, bear in mind that the allergen that gets you may not be the one you see every day. “It’s not necessarily the tree in your backyard,” Ogbogu says. “It may be the maple tree 5 miles away. It’s the region, not the perimeter of your property.”