Yep, Allergies Might Be to Blame for Your Upset Stomach—Here's What to Know

Woman blowing her nose.

If you suspect you have seasonal allergies you’re not alone: the Asthma and Allergy Foundation of America notes that over 24 million Americans experience the same thing. While seasonal allergies often begin in the sinuses, you may also experience symptoms in your head (headache and pressure), throat and chest (hoarseness and cough) and yes, even in your stomach (in the form of gastrointestinal or GI distress).

But how do you know if you're feeling sick because of higher seasonal pollen counts or simply from the result of last night’s meal? Here’s what is going on in your gut during allergy season, and how to prevent an upset stomach when seasonal allergies abound.

Can Seasonal Allergies Make You Feel Sick?

There is evidence that adults with seasonal allergies have a unique gut microbiome—which includes the population of bacteria in the digestive system—compared with those who don’t experience seasonal allergies. One such study from 2015 was conducted as part of the American Gut Project and found a low diversity of gut bacteria.

In addition, seasonal allergies are known to cause sinus inflammation, but that isn’t the only area that can become inflamed. In fact, Dr. Shawn Nasseri, MD, ENT-otolaryngologist based in Los Angeles and co-founder of Euka, notes that during seasonal allergies, foods may be consumed that can cause inflammation in the airways, skin, and in our gut.

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“This means you can ‘stack’ minor, otherwise inconsequential allergic reactions together with seasonal pollen and allergens that can cause an increase in allergy symptoms,” continues Dr. Nasseri. “Histamine is released in the body and enters the gastrointestinal tract, which can cause gas, bloating, nausea, stomach pains and diarrhea.”

He notes specific foods that can make seasonal allergy symptoms worse may include

  • Wheat

  • Berries

  • Alcohol

  • Nightshades (including tomatoes, eggplant and persimmon)

A 2014 study published in Clinical and Translational Allergy specifically examined adults whose seasonal allergies included birch pollen; they were found to have marked inflammation in the intestine, which was aggravated seasonally.

Another potential cause of stomach distress due to allergies is post-nasal drip, which can also affect the throat and chest. According to Dr. Clifford Bassett, MD, allergist at NYU Langone Health based in New York City, this accumulated nasal mucus can also lead to excessive coughing, which in rare instances may induce vomiting.

Signs Seasonal Allergies are the Cause of GI Distress

Because an upset stomach isn’t exclusive to seasonal allergies, it can be hard to pinpoint exactly when GI distress is a result of any allergies you may be experiencing. Some of this will involve keeping track of your symptoms when seasonal allergies flare up, to pinpoint if an upset stomach is regularly occurring—either due to inflammation or in specific periods when your mucus production is increased.

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“Different allergens and pollen spike throughout the year, and it can sometimes be difficult to diagnose gastrointestinal issues due to seasonal allergies because oftentimes upper respiratory symptoms such as sneezing, coughing or runny nose, won’t occur with an upset stomach,” admits Dr. Nasseri. “If you do not usually experience an upset stomach or notice that these symptoms are worse during certain times of the year, you can usually attribute it to seasonal allergies.”

How to Treat Upset Stomach Caused by Seasonal Allergies

In this case, reducing your stomach upset caused by seasonal allergies often requires treating the seasonal allergies themselves. Dr. Bassett first recommends visiting an allergist for in-office testing, which can help identify your triggers.

“[This allows] a more tailored treatment for an allergy sufferer,” explains Dr. Bassett. “I have found the most successful approach is to be ‘proactive,’ that is [to] start their allergy treatment(s) early before the peak pollen season kicks into high gear.”

Another preventative method is to reduce your gut inflammation during peak allergy seasons. Besides avoiding the foods Dr. Nasseri mentioned, research out of Stanford University from 2021 notes that a diet high in fermented foods can not only diversify gut bacteria but also help reduce inflammatory markers.

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“With increased inflammation, there tends to be an increase in mucus production,” explains Dr. Nasseri. “Focus on anti-inflammatory foods to limit the overproduction of histamine, which our bodies release to fight the ‘invaders’ and result in our allergy symptoms.”

Treating allergy symptoms with over-the-counter medication, saline spray, and, if warranted, allergy medication or injections from your doctor, may also help reduce GI symptoms as a result.

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