What can trigger IBS?

Irritable bowel syndrome (IBS) is a common disorder that affects the large intestine (colon). IBS causes symptoms like abdominal cramping, bloating, and changes in bowel habits. These symptoms can vary from person to person and range from mild to severe. IBS is a chronic condition that requires long-term management. Understanding what can trigger IBS symptoms is an important part of managing the condition.


Diet is one of the most common IBS triggers. Certain foods and drinks can stimulate the gastrointestinal (GI) tract and make IBS symptoms worse. Some common dietary triggers include:

  • Fatty foods – High-fat foods take longer to digest and can cause abdominal cramping and diarrhea in people with IBS. Foods high in fat include fried foods, pizza, whole milk, and cheese.
  • Gas-producing foods – Foods that produce gas as they are broken down can cause bloating, cramps, and flatulence. These foods include beans, lentils, broccoli, cabbage, cauliflower, carbonated drinks, and apples.
  • Gluten – Some people with IBS are sensitive to gluten, a protein found in wheat, barley and rye. Gluten can damage the lining of the small intestine and cause diarrhea, bloating, cramping, and fatigue.
  • FODMAPs – These fermentable carbohydrates can be difficult to digest and rapidly increase fluid and gas in the intestine. Foods high in FODMAPs include wheat products, beans, vegetables, fruits, and dairy products.
  • Caffeine – Found in coffee, tea, soda, and chocolate, caffeine can stimulate the intestines and worsen diarrhea. Caffeine withdrawal can also cause headaches, fatigue, and depression.
  • Alcohol – Alcohol irritates the stomach lining, increases acid production, and speeds up stool moving through the colon, resulting in diarrhea. It can also impair nutrient absorption.
  • Spicy foods – Heavily spiced foods containing hot peppers or black pepper may irritate the stomach lining and trigger cramping and diarrhea in those with IBS.
  • Sugar-free sweeteners – Sorbitol and mannitol sugar alcohols found in sugar-free gum and candies can cause bloating and diarrhea.

Eating large meals can also put strain on the digestive system and bring on symptoms in some people with IBS. Eating smaller, more frequent meals may help minimize issues.

Stress and Anxiety

There is a strong connection between the brain and the gut. Stress and anxiety can disrupt normal GI functioning and trigger IBS symptoms like diarrhea, constipation, cramping, and bloating. Stress causes the body to release hormones that speed up digestion. Anxiety activates the nervous system, which can stimulate intestinal spasms. Those with IBS may find their symptoms get worse during stressful life events.


Hormonal changes related to the menstrual cycle, birth control pills, and menopause can provoke IBS symptoms in some women. During menstruation, progesterone levels drop rapidly, which can trigger abdominal cramping and loose stools. Hormones likely influence the sensitivity of nerve fibers in the colon, making the GI tract more reactive. Women with IBS often find symptoms most troublesome during or around their periods.


Certain medications like antibiotics, antidepressants, iron supplements, osteoporosis drugs, and antacids containing calcium or aluminum can impact gut motility and worsen IBS symptoms. Common medication triggers include:

  • Antibiotics – Antibiotics alter the balance of good and bad bacteria in the gut, which can disrupt normal digestion and lead to abdominal discomfort, bloating, and diarrhea.
  • Antidepressants – Medications like tricyclic antidepressants and SSRI antidepressants affect neurotransmitters involved in GI functioning and may provoke diarrhea or constipation.
  • Antacids – Calcium and aluminum-containing antacids reduce stomach acid, which is needed to properly break down and absorb nutrients. This can result in diarrhea.
  • Iron supplements – High dose iron tablets can further irritate the intestines and worsen diarrhea and cramping in people with IBS.
  • Osteoporosis drugs – Bisphosphonates like alendronate (Fosamax) and risedronate (Actonel) have GI side effects including nausea, heartburn, and diarrhea.

Talk to your doctor about managing side effects if you have to take one of these medications on an ongoing basis.


Bacterial and viral infections that cause gastroenteritis, or inflammation of the stomach and intestines, can lead to persistent changes in bowel habits and function. Post-infectious IBS can develop after an acute gastrointestinal infection. The immune system and gut microbiome may be altered, resulting in chronic diarrhea or constipation.

Common infections implicated in post-infectious IBS include:

  • Norovirus – This highly contagious virus causes inflammation in the stomach and intestines, diarrhea, nausea, and vomiting.
  • Salmonella – Food poisoning from Salmonella bacteria leads to severe diarrhea, fever, and abdominal cramps.
  • Campylobacter – A bacterial infection resulting in cramping, diarrhea, nausea, and vomiting.
  • Shigella – Shigella bacteria invade the intestinal lining and cause bloody diarrhea, fever, and fatigue.
  • E. coli – Certain strains of Escherichia coli cause acute diarrhea that can progress to hemorrhagic colitis.

Those who experience an acute gastrointestinal infection are at risk of developing post-infectious IBS. Symptoms may persist for months or years after the infection has resolved.

Small Intestinal Bacterial Overgrowth

Small intestinal bacterial overgrowth (SIBO) occurs when excessive bacteria grow in the small intestine. This can cause bloating, abdominal pain, diarrhea, and nutritional deficiencies. SIBO is more prevalent in people with IBS compared to healthy controls, affecting up to 84% of those with IBS.

When bacteria overgrow in the small intestine, it leads to increased fermentation and gas production. Symptoms of SIBO mirror those of IBS. Studies have found that treating SIBO with antibiotics improves IBS symptoms for some people.

Food Intolerances

While not conclusively proven, some experts theorize that certain food intolerances like lactose intolerance may contribute to IBS symptoms. People with lactose intolerance lack the enzyme need to properly digest lactose, the sugar found in dairy products. This can result in bloating, cramps, and diarrhea after consuming milk, yogurt, soft cheeses, and ice cream.

Removing lactose from the diet may relieve symptoms for some people with IBS. However, lactose intolerance rarely accounts for all IBS symptoms. Those with celiac disease are also more prone to developing IBS, likely due to chronic inflammation in the intestines.

Changes in Gut Microbiota

There is growing evidence that changes and imbalances in the community of microorganisms in the gut (gut microbiota) contribute to IBS. The microbiota assists with food digestion, produces vitamins, and protects against infection.

Those with IBS seem to have a different makeup of gut bacteria compared to healthy people. Research indicates IBS patients have reduced bacterial diversity and fewer beneficial Bifidobacteria and Lactobacillus species. Increased levels of “pro-inflammatory” bacteria have also been observed.

Alterations in the gut microbiota could influence motility, increase intestinal permeability, and activate immune responses in ways that exacerbate IBS symptoms.

Genetics and Family History

IBS tends to run in families, suggesting genetics play a role. Having a close relative with IBS increases your risk two to threefold. Specific genes involved with serotonin signaling, immunity, and the gut microbiome may make some people more vulnerable.

Research has identified 38 different genes that may be associated with IBS risk. Variations in these genes affect how the gut and nervous system interact and increase susceptibility to developing IBS after infection, stress, or other triggers.

Intestinal Motility Issues

Abnormalities in the colon’s ability to contract and move contents through the GI tract (intestinal motility) are commonly found in people with IBS. The colon may be overly sensitive and contract too frequently or exhibit weak, uncoordinated contractions.

This can slow down transit and cause constipation, or accelerate transit and provoke diarrhea. Nerves and muscles controlling motility may overreact to triggers like foods or stress in those predisposed to IBS.


There is some evidence that inflammation in the GI tract associated with celiac disease, food allergies, or post-infectious IBS may contribute to the development of IBS. Increased infiltration of immune cells like mast cells and lymphocytes has been found in the intestines of some IBS patients.

The release of inflammatory substances like histamine and cytokines in the intestinal lining may enhance sensitivity to pain and contribute to disordered motility seen in IBS.

Intestinal Hypersensitivity

Visceral hypersensitivity helps explain why low-grade inflammation or insignificant distension in the intestines can provoke pain and discomfort in IBS patients. Nerves in the colon appear overly reactive, and mildly abnormal bowel responses are perceived as painful spasms.

Altered signaling between the gut and brain may lower the threshold for triggering IBS symptoms. This may relate to changes in gut microbes, genes involved in serotonin regulation, or chronic low-grade inflammation.

Psychological Factors

Although stress and anxiety do not cause IBS per se, they can exacerbate and trigger symptoms. Psychiatric conditions like depression, panic disorders, and post-traumatic stress disorder occur more commonly in those with IBS compared to the general public.

Difficult early life events like childhood trauma or abuse also increase adult risk of developing IBS. Brain mechanisms that process emotions and stress can increase gut sensitivity and the severity of IBS symptoms.


While the exact causes are still unclear, IBS is the result of complex interactions between the gut, brain, nerves, immune system, hormones, diet, genetics, and environmental factors. There are many potential triggers that can incite symptoms in those genetically predisposed to developing IBS.

Diet, stress, hormones, gut infections, antibiotics, and intestinal oversensitivity all seem to play a role in the pathogenesis. However, these factors may differ between individuals. Symptoms can fluctuate over time and change in response to influences like foods, stressors, and hormonal shifts.

Often it is a combination of multiple underlying issues that leads to the development of IBS. Awareness of common triggers allows individuals to effectively manage symptoms by controlling flare factors through diet modifications, stress reduction, probiotics, and other lifestyle measures.

Leave a Comment