Most people with IBS know the pattern: a run of bad days, then a calmer stretch. Diary research confirms that this isn't imagined. IBS symptoms cluster into episodes rather than striking at random, and each type of symptom has its own typical length.[1] Researchers haven't agreed on a definition of a "flare," though, so the figures below are averages from careful symptom diaries, not a timetable your body has to follow.
What does the research say about flare length?
The best data come from a US study in which 124 people with IBS rated every bowel movement on the Bristol Stool Form Scale and scored their pain and bloating each evening, for an average of 73 days, while off laxatives, antidiarrheals and IBS medicines.[1]
| Symptom | How an episode was defined | Average length |
|---|---|---|
| Diarrhea | Two or more loose or watery stools close together | 2.1 days |
| Pain | Days with pain above 3 on a 0–10 scale | 3.1 days |
| Bloating | Days with bloating above 3 on a 0–10 scale | 3.5 days |
| Constipation | Two or more hard or lumpy stools close together, or 3+ days without a bowel movement | 4.5 days |
Two findings stand out. Symptoms don't always arrive together: only 42% of constipation-episode days and 67% of diarrhea-episode days were also pain days, and more than half of pain episodes happened outside spells of diarrhea or constipation.[1] And averages hide a wide range. A Spanish study that tracked symptoms daily over two four-week periods found high-intensity symptoms on more than half of the days, so some people spend long stretches in what feels like one continuous flare.[2]
Why do IBS symptoms come and go?
IBS is a disorder of gut–brain interaction, and UK guidelines describe its symptoms as recurrent and fluctuating, set off by stress, other illnesses, medicines and, often, by eating.[3] The main drivers are:
- Food. FODMAPs (fermentable oligo-, di-, monosaccharides and polyols) are poorly absorbed carbohydrates. In a blinded trial, fructose and fructans brought on symptoms in a dose-dependent way: the more people had, the worse they felt.[4] So several moderate servings close together can add up, or "stack," into a bigger dose. See what triggers IBS flare-ups.
- Stress. In a study that followed 117 outpatients for 16 months, the level of chronic life stress strongly predicted how severe symptoms were later on.[5]
- Sleep. In a small study of women with IBS, a poorer night's sleep predicted more abdominal pain, anxiety and fatigue the next day.[6]
- Hormones. Pain, bloating and changes in bowel habits tend to increase just before and during menstruation, when estrogen and progesterone fall.[7]
- Other illnesses and medicines, which guidelines list among common triggers.[3]
When several of these line up, such as a stressful week, short nights and a run of restaurant meals before your period, a flare is more likely and may last longer. Often no single cause can be pinned down.
Can IBS switch between diarrhea and constipation?
Yes, and that's part of why IBS seems to come and go. In a year-long study of 317 women, more than 75% moved into a different subtype at least once, although only 29% switched between the diarrhea and constipation subtypes.[8] In a UK study, the subtype changed within 12 months in about a third (32%) of people who still met the Rome IV criteria for IBS.[9]
What can shorten a flare?
We found no trials that measured how long flares last with and without treatment, but guidelines list options that ease the symptoms of a bad spell:[3]
- peppermint oil or certain antispasmodics for pain and overall symptoms;
- loperamide for diarrhea, with careful dosing because it can cause pain, bloating and constipation;
- soluble fiber, such as psyllium, built up slowly for long-term control.
Ask a pharmacist or doctor which products suit you. For practical steps during a flare, see how to calm an IBS flare-up and what to eat during a flare.
How can you learn your own flare pattern?
The diary method from the research works for you too. Note the day each flare starts and ends, the main symptom and its severity, your stool type, and what was happening in the days before: meals, sleep, stress, illness, new medicines and, if relevant, your cycle day. After a few months you'll see how long your flares usually last and what tends to come before them. IBS Clue keeps quick symptom check-ins with severity, a Bristol stool log and a meal log in one place, which makes those patterns easier to spot. Our guide to keeping an IBS food diary explains what to record.
When to see a doctor
See a doctor if a flare is much longer, more severe or different from your usual pattern, or if you have any of these features, which aren't caused by IBS:[10][11]
- blood in your stool, or black stools
- unintentional weight loss or anemia
- fever
- pain or diarrhea that wakes you at night
- a family history of bowel cancer, inflammatory bowel disease or celiac disease
- symptoms that start after about age 50
More detail is in IBS red flags.