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Spring brings warmer temperatures, blooming flowers and, for millions of Americans, the arrival of allergy season. It also coincides this year with the arrival of COVID-19, which could make allergy sufferers hyperaware of every sneeze and sniffle.

But there are key differences in symptoms. Seasonal allergies can cause sneezing, runny nose, itchy eyes and cough. Yet unlike allergies, a fever, with other symptoms including cough and shortness of breath.

When seeking relief, people with allergies who are concerned about heart disease or high blood pressure must be especially careful when taking blood pressure-raising, over-the-counter decongestants. They're also stimulants, which can increase heart rate.

But determining the extent of the direct connection between allergies and heart health is a topic that needs more research. A look at two studies offers examples of differing conclusions.

A 2016 study in the examined the relationship between airborne allergen concentrations and emergency room visits for heart attacks in Ontario, Canada, from 2004-2011. The study found the risk of having a heart attack was 5.5% higher on days with the highest pollen levels compared to days with the lowest levels. Heart attack risk was highest in May and June, when tree and grass pollen are most common.

"There appears to be an association between seasonal allergies and cardiovascular health," said Dr. Laurence Sperling, the Katz Professor in Preventive Cardiology at Emory University School of Medicine in Atlanta. "This is an area where further investigation is needed."

The results contrast to findings from another 2016 study in the , which found patients with physician-diagnosed allergic rhinitis, or hay fever, had a significantly lower risk for heart attack than patients without hay fever. That study looked at Kaiser Permanente Southern California patients from 1999-2012.

"Other allergic conditions such as asthma have been shown in several studies to have an increased risk of cardiovascular disease, so it was a little surprising to us that we found this association," said Dr. Angelina Crans Yoon, the study's lead author. "We thought frankly it would be the opposite."

Crans Yoon, an allergist and immunologist, said patients were still more likely to have high blood pressure, despite a smaller chance for heart attack. "Since then, a couple other studies have come out that kind of show a similar association," she said.

One potential reason for her study's findings, she said, was patients with hay fever had more frequent visits to the doctor, which could lead to more blood pressure screenings. In turn, that could lead to a patient being prescribed medication to reduce high blood pressure.

Like Sperling, Crans Yoon said the topic overall needs more research. Risk factors for cardiovascular disease can build over time, so even studies that follow patients for more than a decade may not capture a complete picture.

And her advice for patients still hasn't changed.

"It's not that having the allergies or suffering through it makes you stronger or anything like that," said Crans Yoon, of Dignity Health Medical Foundation in Davis, California.

"Working to reduce your cardiovascular risk factors – eating a healthy diet, exercising and getting enough sleep – all those things that are important for your overall health are still very important whether you have allergies or not," she said.

Other general tips for allergy sufferers:

– Keep doors and windows closed and run the air conditioner during pollen season.

– Change clothes and take a shower after being outside.

– Antihistamines can help clear congestion and are safer for the heart than decongestants.

"Individuals with high blood pressure or known heart disease should be cautious with, or avoid, decongestants," Sperling said. "It is always a good idea to check with your doctor before taking an over-the-counter medication for seasonal allergies."

Seeing a physician or allergist can also help people identify allergy triggers, Crans Yoon said, which can help allergy sufferers reduce exposure and anticipate when to take medication.

If you think you have more than just allergies, contact your physician and follow guidelines from the Centers for Disease Control and Prevention about