Allergies and Diarrhea: Causes, Symptoms, and Treatment


Can seasonal allergies cause diarrhea?

Seasonal allergies can cause diarrhea because the histamine your body releases can cause gastrointestinal upset. Your gut is lined with cells that have receptors for histamine. When histamine binds to these receptors, it can cause muscle contractions in the digestive system, leading to abdominal cramps and diarrhea.

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It's no secret that allergies can be annoying, with symptoms like itchy eyes, a runny nose, and sneezing. But can allergies cause diarrhea? Yes, your allergies can also manifest as uncomfortable gastrointestinal symptoms.

Diarrhea isn't usually the first thing that comes to mind when considering allergy symptoms. However, an overactive immune system can be the culprit behind this type of distress. The link between allergies and diarrhea means that your stomach may not stop churning when the pollen count is high.

Read on to learn how and why allergies can disrupt your digestive system, causing symptoms like diarrhea, and how to find relief.

The Connection Between Allergies and Diarrhea

The link between allergies and diarrhea is complex and extends beyond food allergies. You can experience stomach issues even if you don't have a food allergy. Exposure to allergens such as pollen, dust mites, mold, and pet dander can also cause allergic reactions that lead to this symptom.

How Do Allergies Cause Diarrhea?

If you're allergic to something, you might wonder whether it can cause diarrhea. The answer is yes—allergies can cause gastrointestinal problems. There are various ways in which allergies can affect your digestive system and lead to diarrhea.

Pollen Food Allergy Syndrome

When you eat something that your body is allergic to, it will release histamine into the gut in an attempt to get rid of the offending ingredient. This can cause symptoms such as diarrhea.

Pollen food allergy syndrome (PFAS) can also cause diarrhea. This is a condition in which the body's immune system mistakenly identifies proteins found in certain foods as similar to pollen proteins. For instance, if you're allergic to birch pollen, you may experience PFAS when eating celery, peanuts, hazelnuts, almonds, fennel, or apples. Likewise, if you're allergic to ragweed pollen, you may react to bananas, zucchini, melons, or cantaloupe.

If you have pollen food allergy syndrome, certain fresh vegetables and fruits, spices, and nuts will trigger an allergic reaction that will cause itching and swelling of the lips, mouth, and tongue. Research published in the American Journal of Gastroenterology shows that PFSA can cause abdominal pain and diarrhea. The study found that the symptoms of PFAS are similar to those of irritable bowel syndrome (IBS), which include bloating and diarrhea.

Seasonal Allergies

It's also possible for seasonal allergies to cause diarrhea. Allergens, such as pollen, can trigger an allergic reaction in the body that affects the digestive system. This can lead to stomach cramps, nausea, constipation, diarrhea, and GERD.

What's the Difference Between Food Allergies and Intolerances?

It's common for people to confuse food allergies with food intolerances. While the two conditions can cause similar symptoms, they are triggered by different mechanisms. Food allergies result from an overreaction of the immune system to particular food substances. The primary cause of food allergies is proteins.

Proteins are found in peanuts, tree nuts, chicken eggs, dairy, fish, wheat, soy, and shellfish like shrimp.

When your body encounters even small amounts of the offending food, it will release histamine, leading to an allergic reaction. Food allergy symptoms include digestive problems, hives, and swelling of the tongue and lips.

On the contrary, food intolerances are caused by the body's inability to digest certain foods properly. Lactose intolerance is a prime example of this. It occurs when your body does not produce enough of the enzyme lactase to break down the lactose found in dairy products.

Gluten intolerance is another example. If you have gluten intolerance, your body can't properly digest the proteins found in wheat, barley, and rye. Food intolerance causes symptoms like gas, belly pain, nausea, diarrhea, and bloating.

What Else Causes Diarrhea?

Besides allergies, several other conditions can cause diarrhea. These include:

Bacteria from Contaminated Food or Water

Bacterial contamination of food or water is one of the most common causes of diarrhea. Contaminated food or water can contain harmful bacteria such as salmonella, E. coli, and shigella, which can cause severe gastrointestinal distress and lead to diarrhea.


Viral infections such as the flu, norovirus, and rotavirus can cause diarrhea. These viruses attack the digestive system and disrupt its normal functioning, leading to loose stools and other symptoms associated with diarrhea.

Certain Medications

Some medications, such as antibiotics, can cause diarrhea due to the disruption they cause in your gut microbiome. Antibiotics kill off both good and bad bacteria in the body, which can lead to digestive problems like diarrhea.


Parasites like Giardia lamblia can infect your digestive tract and cause symptoms such as diarrhea. They can cause inflammation in the intestines, leading to loose stools and other symptoms associated with diarrhea.

Dietary Issues

Overeating certain foods, such as fried or greasy foods and refined sugar, can cause diarrhea. Eating a high-fiber diet can also lead to diarrhea. High-fiber diets may irritate the digestive system, leading to loose stools.


When your body is stressed, it releases hormones that can affect the digestive system and cause a disruption in normal functioning. The disruption can lead to loose stools and other symptoms associated with diarrhea.

Artificial Sweeteners

Artificial sweeteners such as sorbitol and mannitol are often found in sugar-free products. They can have a laxative effect on some people, leading to diarrhea, especially when consumed in large amounts.

Intestinal Diseases

Some intestinal diseases, such as Crohn's disease and ulcerative colitis, can cause severe diarrhea due to the inflammation they cause in the intestines. The damage they cause to the intestines can disrupt normal functioning, which can cause loose stools and other symptoms associated with diarrhea.

Symptoms of Diarrhea

The most obvious symptom of diarrhea is loose, watery, and frequent bowel movements.

However, you might notice other symptoms, such as:

  • Abdominal pain or cramping
  • Bloating
  • Nausea or vomiting
  • Soreness in the rectal area
  • Dehydration
  • Fever
  • Mucus in the stool
  • Weight loss

It's important to seek medical attention if you experience any of the above symptoms. Your doctor can diagnose the cause and provide treatment to relieve your symptoms.

Risk Factors of Diarrhea

Certain lifestyle factors can increase your risk of developing diarrhea. These include:

  • Poor hygiene
  • Improper food handling
  • Poor nutrition
  • Traveling to places with less-than-optimal sanitation standards
  • Immune system deficiency
  • Age
  • Stress

It's important to talk to your doctor if you think that any of the above factors might be putting you at risk of developing diarrhea.


The proper treatment for diarrhea comes down to the cause. Below are some of the treatment options that you can consider:

Over-The-Counter Anti-Diarrheal Medications

OTC medications such as loperamide or bismuth subsalicylate can reduce the frequency and looseness of your bowel movements. These medications work by slowing down your intestines' movement and reducing the number of restroom trips. They can reduce the fluid in your stool and make it more solid.

Dietary Changes

Dietary changes such as increasing your fiber intake or avoiding foods that irritate the digestive tract can reduce symptoms. The BRAT diet (bananas, rice, applesauce, and toast) is recommended for people with diarrhea. This diet is effective because the foods are bland and easy to digest.


Probiotics are beneficial bacteria that can restore the balance of your gut microbiome, especially when you have antibiotic-associated diarrhea. They repopulate and maintain the natural flora of your digestive tract, which reduces the risk of developing diarrhea. Besides reducing diarrhea, a probiotic supplement can increase your body's natural immunity.

Fluids and Electrolytes

It's important to replace fluids and electrolytes lost due to diarrhea. Drinking clear liquids such as water or sports drinks can help. Your doctor might also prescribe an oral rehydration solution that contains electrolytes like sodium and potassium.


If allergies cause your diarrhea, then antihistamines can help reduce symptoms. Antihistamines block certain chemicals in your body that trigger an allergic reaction. They can reduce swelling in the small intestine and prevent diarrhea.

Sublingual Immunotherapy

Sublingual immunotherapy is a newer and more effective treatment for allergies. It involves placing drops or tablets of allergens under your tongue and gradually increasing the doses to reduce sensitivity. The goal is to desensitize your body to allergens and provide long-term relief from allergy symptoms.


The best way to prevent diarrhea is to practice proper food handling, nutrition, and hygiene. This means washing your hands before handling and eating food and preparing food in a sanitary manner. You should also disinfect surfaces that people often touch and avoid sick people.

Other practices include cooking food well and drinking clean water. If allergies are a trigger for your diarrhea, then avoiding allergens can help. During the allergy season, you should keep windows closed, wear a mask when outdoors, and wash your clothes after being outdoors.

When to See a Doctor

You should see a doctor if you have diarrhea that lasts longer than three days or is accompanied by blood, fever, or cramps. You should also seek medical help if you feel very weak or dehydrated. In this case, you might have a dry mouth and skin, little or no urine, and feel lightheaded.

You should see a doctor for allergies if your symptoms are severe and do not improve with OTC medications. Severe reactions include anaphylaxis, a swollen tongue or throat, trouble breathing, and other asthma-like symptoms.

Your doctor will perform an allergy test to determine which allergens you are sensitive to. They might use the common skin-prick testing method, which involves injecting a small allergen extract into your skin to see how your body reacts. Unfortunately, this test can be uncomfortable due to needle pricks, and you must go to your doctor's office.

An at-home allergy test is a more convenient alternative. Wyndly's at-home allergy test kit requires only a small blood sample that you draw in the comfort of your home with a quick finger prick and send back to Wyndly for testing. Once the allergy doctor interprets the result, you can begin a personalized treatment plan.

Take Our Allergy Assessment

With Wyndly, allergy symptoms don't have to take over your life. Once you take our at-home allergy test, our allergy doctors will create a personalized treatment plan using sublingual immunotherapy to help you live allergy-free.

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