Understanding an ulcerative colitis flare-up

Living with ulcerative colitis often means navigating a cycle of periods when symptoms are calm (remission) and periods when they return or worsen (flares). Understanding what a flare is, what can trigger one, and how to respond can help you manage the condition more effectively.

What is a UC flare?

A flare — sometimes called a relapse or active disease — is when UC symptoms become more intense after a period of remission. During remission, inflammation in the colon is low or absent, and most people can live relatively normal lives. During a flare, that inflammation returns, bringing symptoms along with it.

Flares can be mild, moderate, or severe, and their duration varies widely — some resolve within a few weeks with treatment, others last months. Understanding the full range of ulcerative colitis symptoms can help you recognise a flare early.

Common warning signs a flare is starting

Recognizing a flare early can help you contact your doctor before symptoms become severe. Early warning signs include:

• Increasing stool frequency (more trips to the bathroom than usual)
• Return of blood in stool after it was absent
• More abdominal cramping or pain than your baseline
• Looser or more urgent stools
• Fatigue that gets worse despite adequate rest
• Returning night-time bathroom trips
• Appetite loss or nausea

These signs do not always mean a major flare is coming — but they warrant a call to your gastroenterologist rather than waiting for your next scheduled appointment.

What triggers UC flares?

Not everyone has the same triggers, and flares do not always have an obvious cause. However, common factors associated with flares include:

Stopping or changing medication

Missing doses of UC medication — even briefly — is one of the most common reasons people flare. Mesalamine and other maintenance medications are intended to be taken consistently, not just during active symptoms. If mesalamine alone is not controlling your disease, read about what to do when mesalamine is not working.

Infections and illness

Bacterial or viral infections, including gastrointestinal bugs, can trigger UC flares. Certain bacteria (like C. difficile) can cause flares directly by infecting the colon.

Non-steroidal anti-inflammatory drugs (NSAIDs)

Medications like ibuprofen (Advil, Motrin) and naproxen (Aleve) can irritate the gut lining and trigger or worsen UC symptoms. If you regularly take NSAIDs for pain or other conditions, discuss alternatives with your doctor.

Antibiotics

Antibiotics alter the gut microbiome and can sometimes trigger a UC flare. If you need to take antibiotics, let your gastroenterologist know.

Stress

The gut-brain connection is real. Psychological stress does not cause UC, but it can worsen symptoms and may contribute to flares in people whose disease is otherwise controlled. Stress management strategies — sleep, exercise, and mental health support — can be part of an overall UC management plan.

Diet

No specific diet causes UC, but certain foods may aggravate symptoms during a flare. High-fiber raw vegetables, dairy (for people with lactose sensitivity), spicy foods, alcohol, and caffeine are common triggers for some patients during active disease. See our guide on what to eat during an ulcerative colitis flare for practical guidance.

How flares are assessed

When you contact your doctor about possible flare symptoms, they may:

• Ask about stool frequency, blood, pain, and urgency
• Order blood tests to check inflammation markers (CRP, ESR) and rule out anemia
• Order a stool test to rule out infection (especially C. difficile)
• Request a fecal calprotectin test to measure intestinal inflammation
• Consider a flexible sigmoidoscopy or colonoscopy if the picture is unclear

The goal is to confirm that it is a UC flare (rather than an infection or other cause) before adjusting treatment.

How flares are treated

Treatment depends on the severity of the flare and your current medication:

• Mild to moderate flares: May be managed with increased doses of your current medication, adding rectal therapies (suppositories or enemas), or a short course of steroids
• Moderate to severe flares: May require oral or intravenous corticosteroids, stepping up to a biologic or JAK inhibitor, or hospitalization in severe cases
• Refractory flares: If medications are not working, your gastroenterologist may discuss surgical options

Your doctor will guide this decision based on your individual history and how you respond to initial treatment. For a full overview of treatment options, see ulcerative colitis treatment options.

What you can do during a flare

While waiting to see your doctor or while receiving treatment:

• Stay hydrated — diarrhea causes fluid and electrolyte loss
• Eat easy-to-digest foods (see our guide on what to eat during a UC flare)
• Rest when possible
• Avoid NSAIDs for pain — acetaminophen (paracetamol) is generally safer, but check with your doctor
• Track your symptoms (stool frequency, blood, pain scale) to share with your doctor
• Do not stop your maintenance medications without guidance — stopping them can worsen the flare

Questions to ask your GI doctor

• Do my current symptoms suggest I am in a flare — and how severe?
• Should we do any tests to confirm: stool test, blood test, or scope?
• Do we need to adjust my current medication dose?
• Is a short course of steroids appropriate for this flare?
• Are there specific triggers I should be working to identify or avoid?
• What symptoms would mean I need to call your office urgently rather than wait?
• If my current treatment is not controlling flares, what are my next options?

When to seek urgent care

Contact your doctor same-day or seek urgent care if you experience:

• Significantly increased rectal bleeding
• Fever above 38.5°C / 101.3°F
• Severe abdominal pain
• Inability to keep fluids down
• Feeling faint or very weak

Seek emergency care immediately for heavy bleeding, signs of dehydration, or rapidly worsening symptoms.

This content is for educational purposes only. It is not a substitute for advice from a licensed healthcare provider.