“How long will this last?” is the first question most people ask in a flare, and the honest answer has two halves. There is no fixed duration — but there is a reliable pattern, and most of what determines where you land in it happens in the first week.
The usual timeline
With treatment started promptly:
| Days 3–5 | First improvement on oral steroids: fewer trips, less blood |
| Weeks 1–2 | Most people notice a clear change |
| Weeks 2–8 | The flare settles; steroids taper over roughly eight weeks |
| Weeks 4–8 | Aminosalicylates reach full effect, if that is the route used |
| Beyond | Fatigue often outlasts the bowel symptoms by several weeks |
Without treatment, there is no comparable table. Some mild flares — particularly proctitis — do quieten by themselves. Many do not, and can grind on for months.
Why the medication route changes the answer
The same flare treated two different ways runs on two different clocks.
Aminosalicylates (mesalazine and similar) are the first line for mild to moderate disease and work gradually. NICE’s guidance expects them to be given time: four weeks before deciding they have failed, and up to eight weeks for full benefit. They are slow but they are also what keeps you in remission afterwards.
Steroids are fast and are for getting a flare under control, not for staying on. Oral prednisolone generally starts working in three to five days. It is then tapered rather than stopped, usually over about eight weeks, because stopping abruptly risks both an adrenal problem and an immediate relapse.
Topical treatment matters more than people expect. For disease limited to the rectum or left colon, a suppository or enema puts the drug directly where the inflammation is and often works faster and better than tablets. If you have proctitis and have only ever been given tablets, that is a reasonable thing to raise.
The flare that is on a different clock
Acute severe ulcerative colitis is not a bad version of a normal flare. It is a separate, time-critical situation, and its timeline is measured in days.
The threshold is the Truelove and Witts definition: six or more bloody stools a day, plus at least one of fever, a pulse over 90, anaemia or a raised ESR. That combination needs hospital admission, not a GP appointment next week.
In hospital, intravenous steroids are started and the response is formally assessed on day three. This is not arbitrary. Roughly a third of people will not have responded adequately by then, and that group needs rescue therapy — infliximab or ciclosporin — or a surgical opinion. Continuing to wait and hope, in that situation, is what leads to the complications everyone is trying to avoid.
Knowing that day three exists is genuinely useful if you are the one in the bed. It is reasonable to ask: what are my stool frequency and CRP today, and what is the plan if I have not responded by Thursday?
What makes a flare drag
Some of these you can influence and some you cannot.
Within your control:
- Taking maintenance medication. Stopping mesalazine when you feel well is the commonest avoidable cause of a long flare. Maintenance treatment is also what reduces the long-term cancer risk, so it earns its place twice.
- NSAIDs. Ibuprofen, naproxen, diclofenac and aspirin at painkilling doses can trigger or prolong a flare. Paracetamol is the safer option.
- Getting help early. The strongest determinant of how long a flare lasts is how quickly it was treated.
Not within your control:
- Extent. Pancolitis generally takes longer to settle than proctitis.
- An overlapping infection. C. difficile is the one to look out for and is specifically tested for in a flare that will not budge, because treating it as colitis alone will not work.
- Previous steroid exposure. Repeated courses over time tend to predict a more stubborn disease pattern.
Smoking is the oddity. Smoking makes Crohn’s considerably worse, but in ulcerative colitis stopping sometimes coincides with a flare. This is not a reason to smoke — the cardiovascular and cancer harms vastly outweigh any bowel effect — but it is worth mentioning to your team if a flare followed quitting, because they may adjust your maintenance treatment during that period.
The part that outlasts the flare
Bleeding and frequency usually recover first. Fatigue is the straggler, and it often has a specific, fixable cause: iron deficiency from weeks of blood loss, or low B12 or folate.
After a flare has settled, ask for iron, ferritin, folate and B12 to be checked. Correcting an iron deficiency frequently does more for how you feel than anything else at that stage, and it is routinely overlooked once the dramatic symptoms have stopped.
When to stop waiting
Same-day assessment — A&E or 111 — for:
- Six or more bloody stools a day with fever, faintness or a racing pulse.
- Severe abdominal pain with a swollen, hard, tender abdomen.
- Heavy continuous bleeding, or not being able to keep fluids down.
Contact your IBD team this week if:
- A week of adequate treatment has produced no meaningful change.
- A flare has returned within weeks of finishing steroids — that usually means the maintenance plan needs rethinking rather than another steroid course.
- You are on a second or third steroid course in a year. NICE regards repeated steroid dependence as the signal to move to a different maintenance strategy, not to keep prescribing steroids.
Most IBD services run a nurse-led advice line. If you have one, that number is the single most useful thing to have saved before you need it.
