Familiar IBS symptoms often flare and settle on their own, but new, severe, or unusual symptoms shouldn't automatically be blamed on IBS. A flare-up is a stretch when abdominal pain, bloating, or changes in bowel habits intensify beyond your usual pattern.
Food, stress, hormones, sleep, infections, and gut bacteria can all play a role, and often no single trigger explains a flare. Here's what's known about each, what tends to help, and which symptoms need medical attention.
The Gut Mechanism Behind IBS Flare-Ups
IBS doesn't have one single cause. Several processes may contribute, and they vary from person to person.
One is visceral hypersensitivity. This means the nerves in your gut respond more strongly than usual to stretching and contractions. As a result, normal digestive activity can cause pain or a sudden urge to use the bathroom.
Gut motility, the muscular movement that carries food through the digestive tract, can also be faster, slower, or less coordinated than usual. This helps explain why IBS can involve diarrhea, constipation, or alternating between the two.
Serotonin, a signaling chemical found largely in the gut, also helps regulate movement and sensation. Its role in IBS remains an active area of research.
Food Triggers
Different foods can affect your gut in different ways. Paying attention to what you eat and how you feel afterward may help you identify patterns.
High-FODMAP Foods
Onions, garlic, wheat, and some fruits contain fermentable carbohydrates called FODMAPs. These carbohydrates can draw water into the bowel and produce gas as gut bacteria break them down. The resulting pressure and stretching can trigger pain and bloating in people with IBS.
A meta-analysis found that a low-FODMAP diet can improve IBS symptoms for many people. However, a 2025 review found inconsistent results across studies, and not everyone needs to follow the diet.
The low-FODMAP diet is intended as a temporary process of eliminating certain foods, gradually reintroducing them, and identifying which ones you tolerate. Working with a dietitian can help you avoid unnecessary long-term restrictions.
Dairy
Lactose intolerance can occur alongside IBS. If your body has trouble digesting lactose, the sugar in milk, reducing lactose or taking lactase supplements may help. Neither approach works for everyone.
Some dairy products contain less lactose than others. Aged cheeses and some yogurts, for example, may be easier to tolerate than milk. Lactose is also a FODMAP, so dairy-related symptoms can overlap with the effects described above.
Large or Fatty Meals
Eating activates the gastrocolic reflex, which increases contractions in the colon and helps move stool along. Some people with IBS have a stronger response, making them more likely to experience cramping or urgency after eating.
Larger or fattier meals may worsen these symptoms for some people. Smaller meals may be easier to tolerate.
Coffee, Alcohol, and Sugar Alcohols
Coffee can stimulate colon activity, which may contribute to urgency or diarrhea. Alcohol can also affect bowel function, depending on how much you drink and how your body responds. Learn more about alcohol and bowel movements.
Sugar alcohols, including sorbitol and xylitol, are poorly absorbed in the small intestine. They can draw water into the bowel and contribute to gas or diarrhea. Sugar-free gum and candy are common sources.
The Gut Microbiome and IBS
Studies have found differences in gut bacteria in some people with IBS, but everyone shares no single pattern. Researchers also haven't established whether these differences cause symptoms or develop as a result of them.
Changes in gas production and low-grade immune activation are possible explanations for some symptoms. However, these mechanisms are still being studied.
Small Intestinal Bacterial Overgrowth
Small intestinal bacterial overgrowth, or SIBO, occurs when there is an excess of bacteria in the small intestine. It can cause symptoms such as bloating and diarrhea that overlap with IBS.
Researchers continue to debate how often SIBO explains IBS symptoms. Testing and treatment should be guided by a clinician, rather than assuming SIBO is the cause of a flare.
Stress as a Trigger
Stress is one of the most commonly reported IBS triggers. The gut and brain communicate constantly, and stress can affect gut sensitivity, movement, and how strongly you experience digestive sensations. These connections are described in a 2016 review.
Changes in cortisol regulation, which is involved in the body's stress response, are one possible part of this process. However, the role of cortisol in any individual flare isn't fully understood.
Worry about symptoms can also make them feel worse. If you're expecting a flare, you may become more alert to gut sensations that would otherwise go unnoticed. This can contribute to a cycle in which anxiety and digestive symptoms reinforce each other.
The sudden urge to use the bathroom during acute stress is one example. It's sometimes called anxiety poops.
Hormonal and Menstrual Cycle Triggers
Many women with IBS report that their symptoms change throughout the menstrual cycle. Research has found that symptoms often worsen around menstruation.
In one small study of 29 women with IBS, rectal sensitivity increased during menstruation. The reason isn't fully understood, but shifting estrogen and progesterone levels may contribute, and prostaglandins, which influence muscle contractions, may also play a role, according to a 2015 review.
Not everyone experiences the same changes. If your symptoms repeatedly worsen at a particular point in your menstrual cycle, mention the pattern to your doctor.
Poor Sleep and Next-Day Symptoms
Poor sleep may make IBS symptoms worse the following day. A 2024 study found that people with IBS who reported poorer sleep quality tended to experience more abdominal pain the next day.
The relationship wasn't seen in reverse in that study, and sleep measured using a wrist-worn device wasn't linked to symptoms. Because this was one study, it can't establish that poor sleep causes a flare. Sleep and pain processing may share nervous system pathways, but more research is needed to understand the relationship.
Travel and Post-Infectious Triggers
Travel can affect IBS in two main ways: an intestinal infection can lead to lasting symptoms, or changes in your routine can temporarily disrupt bowel habits.
Post-Infectious IBS
Some people develop IBS after an episode of food poisoning or another gastrointestinal infection. This is called post-infectious IBS.
A 2024 meta-analysis found that about 14.5% of people developed IBS at least three months after acute gastroenteritis. Their odds of developing IBS were more than four times those of people who hadn't experienced an infection, although rates varied by infection type.
Possible explanations include lingering inflammation, changes in gut bacteria, and increased gut sensitivity. Symptoms may begin weeks after the original illness, making the connection easy to miss.
Fever, blood in the stool, or severe diarrhea that doesn't improve may point to an ongoing infection or another condition rather than post-infectious IBS. These symptoms need medical assessment.
Travel Without Infection
Travel can also trigger symptoms without an infection. Different foods, changes in meal times, dehydration, and disrupted sleep can all affect bowel habits.
If symptoms are related to changes in your routine, they may ease as you return to your usual schedule. Persistent or unusual symptoms shouldn't automatically be attributed to travel.
Medications and Antibiotics
Antibiotics can disrupt gut bacteria and cause digestive side effects. A 2026 meta-analysis linked antibiotic use, particularly during gastrointestinal infections, with a higher risk of developing IBS. However, the findings don't establish that antibiotics directly cause IBS.
Other medications can affect bowel habits, too. NSAIDs, certain antidepressants, and iron supplements may contribute to diarrhea or constipation, depending on the medication and the person taking it.
If your symptoms change after starting a medication, contact the prescribing clinician. Don't stop a prescribed medication on your own.
When There's No Obvious Trigger
Sometimes, there isn't a clear reason for a flare. IBS involves several interacting systems, so symptoms may worsen without one identifiable trigger.
That can be frustrating, especially when you're trying to prevent another episode. But not finding a cause doesn't mean you're overlooking something obvious. Looking for patterns over several weeks or months may be more useful than trying to explain every individual flare.
