Most people with Crohn’s eventually try to work out what sets off their flares. It is a reasonable instinct, and sometimes it produces a genuinely useful answer. It is also worth saying at the outset that many flares have no identifiable trigger, and that hunting for one after every episode can become a burden in itself.
Here are the triggers with the best evidence behind them, roughly in order of how often they turn out to be the explanation.
1. Stopping or missing medication
This is the most common identifiable cause, and the most preventable.
The logic that leads to it is entirely understandable. You feel well. The drug has side effects, or the injections are a nuisance, or you simply forget during a busy stretch. Nothing happens immediately — so it seems fine.
The problem is that feeling well and being in remission are not the same thing. Studies consistently find significant inflammation in people with no symptoms at all. Maintenance treatment is holding that inflammation down, and when it stops, the process frequently resumes.
There is a second, less obvious risk with biologics. Stopping and restarting raises the chance of developing antibodies against the drug, which can make it permanently less effective. A treatment break can cost you that option for good.
If you want to come off treatment, have that conversation with your IBD team. What does not work well is stopping quietly.
2. Smoking
Smokers with Crohn’s flare more often, need more surgery, relapse sooner after operations and respond less well to biologics than non-smokers.
Quitting changes this measurably. Within a year or so of stopping, flare rates in former smokers move towards those of people who never smoked. Of everything on this list, it is the change with the largest effect.
3. NSAID painkillers
Ibuprofen, naproxen, diclofenac and aspirin can trigger flares. They work by inhibiting prostaglandins, some of which protect the gut lining, and they increase intestinal permeability.
This catches people out because NSAIDs are freely available and widely recommended for exactly the joint pain that often accompanies Crohn’s.
Paracetamol is generally the safer choice. If you need regular anti-inflammatory pain relief — for arthritis associated with your IBD, for example — that is a conversation to have with your gastroenterologist rather than a decision to make at the pharmacy counter.
4. Gut infections
A bout of gastroenteritis can tip a stable Crohn’s patient into a flare. Clostridioides difficile infection deserves particular mention: it is more common in people with IBD, it closely mimics a flare, and it needs completely different treatment.
This is exactly why a stool test is worth doing at the start of a suspected flare. Treating an infection with steroids because it looked like a flare makes things considerably worse.
5. Antibiotics
An awkward one, because antibiotics are sometimes needed to treat Crohn’s complications such as abscesses or perianal disease. But a course of antibiotics disrupts the gut microbiome, and that disruption can precipitate a flare in some people.
Not a reason to refuse antibiotics when they are genuinely indicated — a reason to be aware of the possibility.
6. Stress
Stress does not cause Crohn’s disease. That myth causes real and unnecessary guilt.
What stress does do is influence the gut through established mechanisms: it alters motility, heightens pain perception, affects immune signalling and shifts the microbiome. In practice, many people find their symptoms are genuinely worse during difficult periods, and stress appears to contribute to triggering flares in some people.
The useful framing is that stress is an aggravator rather than a cause. Managing it is worth doing — for quality of life as much as for the disease — but a flare during a hard month is not evidence that you failed to cope well enough.
7. Food
Covered in more detail in our guide to foods to avoid with Crohn’s disease, but the key distinction belongs here too.
Food reliably affects symptoms. Whether it drives the underlying inflammation is much less clear. A meal that leaves you bloated and in pain has not necessarily caused a flare, even though it feels that way.
The practical test: symptoms that settle within a day or two were probably digestive. Symptoms that persist for weeks, with raised calprotectin, are a flare.
8. Hormonal changes
Many women report worse symptoms around menstruation. Pregnancy varies — some find their Crohn’s improves, others find it worsens, and the strongest predictor is how active the disease was at conception. Planning pregnancy while in remission produces better outcomes for both mother and baby, which is worth discussing with your team in advance.
How to tell a flare from something else
Not everything that feels like a flare is one. The common mimics:
| Mimic | How it differs |
|---|---|
| Gut infection | Sudden onset, often with fever or recent travel; stool culture identifies it |
| C. difficile | Usually follows antibiotics; needs a specific test and treatment |
| Bile acid diarrhoea | Common after ileal resection; watery and urgent; responds to bile acid binders |
| Overlapping IBS | Pain and bloating with normal calprotectin |
| Bacterial overgrowth | Bloating and wind, often where there is a stricture |
| Stricture symptoms | Cramping and vomiting after meals, from narrowing rather than active inflammation |
The test that separates most of these is faecal calprotectin. It is simple, non-invasive, and tells you whether there is genuine inflammation behind the symptoms. If you flare regularly, it is reasonable to ask your IBD team whether you can have one done at the start of a suspected flare rather than waiting for a clinic appointment.
What to do when a flare starts
- Contact your IBD team early. Most UK services run an IBD nurse advice line for this. Early treatment shortens flares and reduces lasting damage.
- Do not stop your maintenance medication because it seems not to be working.
- Avoid NSAIDs.
- Keep eating and drinking. Smaller, more frequent, low-residue meals are usually easier. Nutrition matters most when you are least inclined to bother with it.
- Ask for a stool test to rule out infection before escalating treatment.
- Rest, and lower your expectations of yourself for a few weeks.
Seek urgent medical care for severe or constant abdominal pain, persistent vomiting, significant rectal bleeding, a fever above 38°C, or signs of dehydration.
A note on self-blame
The most common thing people get wrong about flares is assuming every one must have a cause they could have avoided. Crohn’s inflammation fluctuates. Sometimes it flares after a stressful month, a missed dose and a takeaway — and sometimes it flares during a calm, well-managed stretch when you did everything right.
Identifying your repeat triggers is genuinely useful. Treating every flare as a personal failing is not, and it adds stress to a condition that stress does not help.
