Key takeaways:
Diarrhea can be a symptom of influenza (the flu). But it’s less common than other flu symptoms, like fever, cough, stuffy nose, and headache.
Children are more likely to have diarrhea when sick with the flu. While adults can also have diarrhea, it’s uncommon.
The best treatments for flu-related diarrhea include drinking plenty of fluids and avoiding foods that can irritate your gut, like spicy or fatty foods. Get medical care if you have signs of dehydration, bloody stools, or diarrhea that doesn’t improve.
Having the flu is never easy. Symptoms tend to come on suddenly and then improve within several days, although coughing and fatigue can last longer. You may already be familiar with common flu symptoms, like fever, fatigue, stuffy nose, and cough. But if you’re also having stomach pain, diarrhea, or nausea, you might wonder whether the flu is responsible.
It turns out that the flu can cause diarrhea, although it’s not very common — especially in adults. If you’re experiencing diarrhea along with flu-like symptoms, here’s what you should know about the possible connection and how to treat it.
Is diarrhea a symptom of the flu?
Yes, diarrhea can be a symptom of the flu. But it’s not very common. Children are more likely than adults to develop diarrhea, nausea, and vomiting when they’re sick with the flu.
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This trend has been reported in medical literature for decades. Children who get sick with influenza B — one of the major strains of influenza virus — are more likely to develop vomiting and diarrhea than those who get sick with influenza A, the other major strain of the influenza virus.
In studies, influenza B causes gastrointestinal symptoms at much higher rates than influenza A. While children sick with influenza A can also develop diarrhea, it’s less common.
Diarrhea and other gut symptoms are generally uncommon in adults with the flu. But they can happen, especially in those who are sick with influenza B and certain strains of influenza A. For example, during the 2009 H1N1 pandemic, about 5% of adults reported diarrhea and other gastrointestinal symptoms. And cases were high again during the 2014-2015 flu season when H3N2, a strain of influenza A, dominated flu season.
Overall, if diarrhea is your main symptom, another illness may be more likely than the flu. This is especially true if you don’t have a cough, sore throat, or congestion.
Why does the flu cause diarrhea?
Scientists don’t know the exact reason why the flu causes diarrhea. The influenza virus mainly infects your upper respiratory tract, and sometimes your lower respiratory tract, too. This is why flu symptoms so often include a cough, congestion, and a stuffy nose.
Researchers have found influenza genetic material in stool and intestinal tissue. But that doesn’t necessarily mean that the virus is actively infecting the intestines. Researchers are still studying how a respiratory infection like the flu can lead to digestive symptoms.
Scientists have suggested a few possible explanations for diarrhea during a flu infection:
Inflammation: Your immune system releases cytokines when you’re sick. These proteins are partly responsible for flu symptoms like headache, fatigue, muscle aches, and fever. This same inflammatory response may also contribute to diarrhea.
Changes in the gut: Some research suggests that the immune response to an infection in your lungs may also affect your gut and upset the balance of bacteria that normally live there. This may lead to diarrhea, even if the virus isn’t directly infecting your gut. Much of this evidence comes from lab and animal studies, so researchers don’t yet know how this may affect people.
Flu medications: Oseltamivir (Tamiflu) and baloxavir marboxil (Xofluza) are FDA-approved oral medications used to treat the flu. Both can cause side effects, including nausea, vomiting, and diarrhea.
Another infection: You can get sick with the flu and another infection at the same time. For example, COVID-19 and gastroenteritis can both cause diarrhea. Depending on your symptoms and recent exposure, you may want to test for COVID or contact a healthcare professional to confirm what’s causing your symptoms.
How long can influenza diarrhea last?
There isn’t a set timeline for flu-related diarrhea. Most flu symptoms last for about 3 to 7 days. But symptoms can last longer, especially if you have a weakened immune system. Flu-related diarrhea usually goes away along with your other flu symptoms. In some cases, it may clear up earlier.
How is the stomach flu different from the flu?
The flu is a respiratory infection caused by the influenza virus. In contrast, the term “stomach flu” refers to gastroenteritis — an infection that irritates your stomach and intestines and causes symptoms like diarrhea, nausea, and vomiting. Several viruses can cause viral gastroenteritis, including norovirus and rotavirus. Influenza viruses don’t cause the “stomach flu.”
Even though both illnesses can cause fever, body aches, and fatigue, they’re distinct infections that usually cause different symptoms:
Influenza (the flu) affects your airways and often causes fever, cough, sore throat, congestion, headache, and body aches.
Viral gastroenteritis (the “stomach flu”) affects your gut and typically causes vomiting, diarrhea, and stomach pain.
Because their symptoms can overlap — especially when diarrhea or nausea appear with the flu — it’s easy to mix them up. But if your main symptoms are stomach cramps, vomiting, and diarrhea without much coughing or congestion, viral gastroenteritis or another digestive illness may be more likely.
How do you treat flu-related diarrhea?
The main goal of treating diarrhea is to prevent dehydration. Young children, older adults, and people with weakened immune systems can become dehydrated more quickly. While it can be difficult to completely stop flu-related diarrhea, these three steps may help you manage it at home.
1. Drink plenty of fluids
Drink fluids throughout the day to replace the water and electrolytes you lose from diarrhea and fever. The best drinks for diarrhea include:
Water
Electrolyte drinks, like Pedialyte, Gatorade, or homemade oral rehydration solution
Broth
No-pulp fruit juice
Avoid alcohol and caffeine, which can worsen diarrhea. Sugary beverages and milk can sometimes worsen diarrhea, so it’s best to avoid these until you’re recovered.
2. Choose light foods
You don’t have to follow a special diet when you have flu-related diarrhea. But you may not have much of an appetite when you’re feeling sick.
When your appetite returns, you can usually resume your normal diet. If your stomach feels unsettled, try starting with small portions of foods that sit well with you.
Try to avoid fried, fatty, and spicy foods. Some people find that bland foods are easier to eat when they feel sick and don’t make their diarrhea worse.
You might try the BRAT diet for a few days, but you don’t need to restrict yourself to it. The BRAT diet focuses on bland, easy-to-digest foods, such as:
White bread
Plain pasta
White rice
Plain crackers
Broth
Applesauce
Cooked cereals
While these foods might not upset your stomach, they’re also not high in fiber or vitamins. So make sure to go back to your usual, varied diet once you start feeling better.
3. Consider over-the-counter medications
An over-the-counter (OTC) probiotic supplement may help when you have diarrhea. Probiotics contain live bacteria and yeast that may help keep your gut healthy. While there’s no evidence that probiotics can make diarrhea go away faster, some people feel better after taking them.
You can also consider taking loperamide (Imodium), an OTC medication that slows the movement of stool through your intestines. Loperamide isn’t recommended for children younger than 5 years.
When to see a healthcare professional for flu-related diarrhea
You can usually manage mild flu-related diarrhea at home. But there are times when you should contact a healthcare professional:
Fever higher than 102°F (39°C)
Signs of dehydration, like very little urine or dark urine
Extreme fatigue or weakness
Intense abdominal pain or rectal pain
Black, tarry, or bloody stool
Diarrhea that lasts longer than 2 days
Frequently asked questions
When a virus causes diarrhea, it can be very contagious. Norovirus, the most common cause of viral diarrhea, spreads quickly from person to person through food, water, and contaminated surfaces or objects. Keep in mind, this is different from influenza, which spreads through respiratory droplets when a person with the infection coughs, sneezes, or talks.
The flu is most contagious during the first 3 days of symptoms. But it can remain contagious for a week or longer. As a good rule of thumb, your flu is no longer contagious once your symptoms are gone and you’re feeling back to normal.
Yes, the flu can cause vomiting. While most people with the flu don’t experience vomiting or diarrhea, these symptoms can occur and are more common in children than adults.
It’s uncommon to get diarrhea after your flu symptoms have resolved. If diarrhea starts after the flu, something other than the flu may be causing it. One common culprit is antibiotics. While antibiotics aren’t used to treat the flu, some people are prescribed antibiotics when they don’t feel well, and antibiotics are a common cause of diarrhea. Viral gastroenteritis, food poisoning, and other medications are also possible causes. If you develop new or severe symptoms after having the flu, talk with a healthcare professional.
When a virus causes diarrhea, it can be very contagious. Norovirus, the most common cause of viral diarrhea, spreads quickly from person to person through food, water, and contaminated surfaces or objects. Keep in mind, this is different from influenza, which spreads through respiratory droplets when a person with the infection coughs, sneezes, or talks.
The flu is most contagious during the first 3 days of symptoms. But it can remain contagious for a week or longer. As a good rule of thumb, your flu is no longer contagious once your symptoms are gone and you’re feeling back to normal.
Yes, the flu can cause vomiting. While most people with the flu don’t experience vomiting or diarrhea, these symptoms can occur and are more common in children than adults.
It’s uncommon to get diarrhea after your flu symptoms have resolved. If diarrhea starts after the flu, something other than the flu may be causing it. One common culprit is antibiotics. While antibiotics aren’t used to treat the flu, some people are prescribed antibiotics when they don’t feel well, and antibiotics are a common cause of diarrhea. Viral gastroenteritis, food poisoning, and other medications are also possible causes. If you develop new or severe symptoms after having the flu, talk with a healthcare professional.
The bottom line
Influenza (the flu) is a respiratory illness caused by influenza viruses. Common symptoms include fever, cough, congestion, headache, and fatigue. But the flu can also cause diarrhea and gastrointestinal symptoms. Children are more likely than adults to have these symptoms.
If you have diarrhea with the flu, focus on replacing fluids en electrolytes and eat a balanced diet as much as you can tolerate. Contact a healthcare professional if you have signs of dehydration, blood stools, intense pain, or diarrhea that doesn’t improve after a couple of days.
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References
Bullock, T. A., et al. (2025). The (digestive) path less traveled: Influenza A virus and the gastrointestinal tract. mBio.
Cao, B., et al. (2009). Clinical features of the initial cases of 2009 pandemic influenza A (H1N1) virus infection in China. The New England Journal of Medicine.
Dilantika, C., et al. (2010). Influenza virus infection among pediatric patients reporting diarrhea and influenza-like illness. BMC Infectious Diseases.
Guo, X. J., et al. (2017). New fronts emerge in the influenza cytokine storm. Seminars in Immunopathology.
Hirose, R., et al. (2016). Long-term detection of seasonal influenza RNA in faeces and intestine. Clinical Microbiology and Infection.
Kaji, M., et al. (2003). Differences in clinical features between influenza A H1N1, A H3N2, and B in adult patients. Respirology.
Minodier, L., et al. (2015). Prevalence of gastrointestinal symptoms in patients with influenza, clinical significance, and pathophysiology of human influenza viruses in faecal samples: What do we know? Virology Journal.
Minton, K. (2014). Sick of the flu. Nature Reviews Immunology.
