How to Know When Ulcerative Colitis Might Be Dangerous: And What to Do About It

There’s a moment many of us with Ulcerative Colitis (UC) know all too well. You’re in the middle of a flare, or maybe just noticing something a little off, and you ask yourself the question:

Is this normal… or is this serious?

It’s a scary space to be in, somewhere between “ride it out” and “should I be at the hospital?” And if you’ve ever tried Googling your symptoms in that moment, you’ll know it can send you spiralling fast.

This blog is here to offer something gentler. A way to tune into your body with more clarity and less panic. I’ll walk you through some of the signs that UC might be getting dangerous, what’s worth flagging to your doctor, and what you can do right now if things feel a bit uncertain.

I’ve lived this. And I believe that the more you understand your condition, the more confident you’ll feel in responding to it.

What Counts as Dangerous with Ulcerative Colitis?

When you live with UC, it’s easy to downplay what your body is going through, especially if you’ve been managing symptoms for a while. But not all flare-ups are created equal. Some symptoms are your body’s way of waving a little red flag that says, “Hey, I need more help.”

So what exactly makes a symptom dangerous?

In simple terms, we’re talking about anything that puts your overall health at risk. That might be:

• Losing too much blood

• Becoming severely dehydrated

• Developing a fever or infection

• Experiencing sudden or severe pain

• Feeling so weak or disoriented, you can’t go about your day

  
  

Sometimes these symptoms signal a complication that needs urgent attention.

But here’s the tricky part: UC is already a complex, fluctuating disease. So, how do you tell when a symptom is just part of a typical flare, and when it’s something more?

That’s what we’re going to break down next.

When Symptoms Cross a Line: What to Watch For

Flare-ups are part of life with UC. But some symptoms go beyond your personal “normal” and might be your body’s way of signalling that something more serious is happening. Here are a few to pay close attention to.

1. Severe or Sudden Bleeding

Seeing blood in the toilet bowl or on your stool can be common with UC, but how much is too much?

If you’re passing large amounts of blood, noticing clots, or feeling lightheaded and dizzy after a bowel movement, it’s time to take it seriously. Significant blood loss can lead to anaemia, fatigue, and in rare cases, more urgent complications like perforation or toxic megacolon.

When to act: Call your doctor if bleeding worsens quickly or is accompanied by faintness or rapid heartbeat. If you're soaking through pads, fainting, or unable to keep fluids down, go to the ER.

Read more on rectal bleeding from the Mayo Clinic

2. Signs of Severe Dehydration

UC-related diarrhoea can make it hard to stay hydrated, especially during a flare. But dehydration isn’t just about being a bit thirsty; it can become dangerous fast.

Look for:

• Dry mouth or cracked lips

• Dark urine (or very little urine)

• Headaches, dizziness, or confusion

• Rapid heart rate

  
  

When to act: If water alone isn’t helping, you’re not urinating, or you feel disoriented, it may be time for IV fluids.

3. Persistent High Fever

A fever during a flare might signal more than just inflammation; it could point to an underlying infection (like C. difficile), an abscess, or a rare but dangerous complication like toxic megacolon.

When to act: Any fever over 38°C (100.4°F) that lasts more than 24 hours or is paired with worsening symptoms needs medical attention. Don’t wait this one out.

4. Intense, Localised Pain

Cramping and discomfort are common with UC, but if the pain is sharp, one-sided, or increasing in severity, that’s a red flag.

This kind of pain could signal a complication like:

• Perforation (a tear in the bowel wall)

• Obstruction

• Severe inflammation causing distension

  
  

When to act: Sudden, severe pain, especially with bloating, fever, or vomiting, is an emergency.

5. Rapid Weight Loss and Malnutrition

Losing a few kilos during a flare isn’t uncommon. But if the weight loss is rapid, involuntary, or paired with signs of nutrient deficiency (like fatigue, hair loss, or muscle wasting), it’s time to step in.

When to act: Bring this up with your doctor if you’ve lost more than 5% of your body weight in a month or are struggling to eat enough to maintain your energy.

6. Fatigue That Feels Like Something More

We all know UC fatigue can be brutal. But if your exhaustion feels bone-deep, like you’re too tired to walk, sit up, or think clearly, it could be a sign that something’s off with your nutrition, iron levels, or even heart rate.

When to act: Mention any extreme or sudden changes in energy, especially if paired with dizziness or brain fog.

Rare but Serious Complications of Ulcerative Colitis

Let’s be clear: most people with UC don’t experience these complications. But knowing what they are, without spiralling into fear, can help you act quickly if something doesn’t feel right.

Think of this as a calm guide to the “just in case” scenarios.

Toxic Megacolon

This is a rare but life-threatening complication where the colon rapidly expands, becomes inflamed, and stops working properly.

Watch for:

• A severely bloated belly

• High fever

• Rapid heart rate

• Pain that gets worse by the hour

• Fewer or no bowel movements despite discomfort

  
  

Emergency warning: Toxic megacolon requires immediate medical attention. Go straight to the ER if you suspect it.

Bowel Perforation (Tear in the Colon Wall)

Perforation is uncommon but serious. It can happen when inflammation weakens the bowel wall, creating a small hole.

Signs might include:

• Sudden, intense abdominal pain

• Rigid or hard belly

• Fever, chills

• Nausea and vomiting

  
  

Emergency warning: This is a surgical emergency. Don’t wait. Get help immediately.

Colorectal Cancer

Having UC doesn’t mean you’ll get colon cancer, but long-term inflammation does slightly raise your risk, especially after 8–10 years of living with the condition.

Lower your risk by:

• Keeping inflammation under control

• Staying on top of your medication

• Getting regular colonoscopies (your doctor will recommend how often)

• 
  

More from the Crohn's & Colitis Foundation on UC and cancer risk 

Osteoporosis from Long-Term Steroid Use

Steroids like prednisone can help manage flares, but long-term use may lead to bone loss.

Protect your bones by:

• Monitoring bone density (especially if you’ve used steroids regularly)

• Taking calcium + vitamin D (if advised by your doctor)

• Including weight-bearing exercise if you’re able

  
  

Outside-the-Gut Symptoms (Extraintestinal Manifestations)

UC doesn’t always stick to the digestive tract. Some people develop issues in other parts of the body, like:

• Eyes: uveitis (pain, redness, blurred vision)

• Joints: arthritis or joint swelling

• Skin: rashes or painful red lumps (like erythema nodosum)

• Liver: primary sclerosing cholangitis (rare, but important to screen for)

  
  

When to act: Report any new or unusual symptoms, especially if they don’t feel gut-related. They might still be connected.

When to See a Doctor Immediately

One of the hardest things about living with Ulcerative Colitis is figuring out when something is “just part of it”… and when it’s something more.

If you’re ever unsure, it’s always okay to check in. You’re not overreacting, you’re responding to a body that’s been through a lot.

Here’s a list of signs that mean it’s time to call your doctor, or in some cases, go straight to the hospital:

Go to the ER or seek urgent care if you have:

• Severe or persistent abdominal pain (especially if it’s sharp or one-sided)

• Heavy rectal bleeding (e.g. filling the toilet bowl or soaking through pads)

• High fever (above 38°C / 100.4°F) that doesn’t go away or gets worse

• Signs of dehydration (dry mouth, no urine, dizziness, confusion)

• Rapid heart rate and shortness of breath

• Severe bloating with no bowel movements

• Sudden confusion, weakness, or inability to stay awake

  
  

Call your doctor if you notice:

• A steady increase in the number of daily bowel movements

• New or worsening blood in your stool

• Unintended weight loss or difficulty eating

• Extreme fatigue that’s interfering with your life

• Any new symptoms outside the gut (eye pain, joint swelling, rashes)

  
  

If you’re ever unsure, start by calling your GP or GI and asking for their guidance. If you can’t get hold of them and the symptoms are worsening fast, rather err on the side of caution.

What You Can Do Right Now (Besides Panic)

Not every worrying symptom means a full-blown emergency. Sometimes, the best thing you can do is slow down, check in, and take practical steps to support your body while you wait for medical guidance.

Here are five things you can do today if you’re feeling unsure, unwell, or somewhere in between:

1. Track Your Symptoms

It might feel basic, but keeping a simple record of your symptoms can help you spot patterns and make sense of changes over time.

Write down:

• Number of bowel movements per day

• Blood or mucus in stool

• Pain levels

• Energy and mood

• Any new or unusual symptoms

  
  

This gives your doctor valuable context and helps you feel more in control.

2. Stay Nourished and Hydrated However You Can

When you’re flaring or feeling unwell, eating and drinking can feel like a challenge.

Focus on:

• Small, frequent sips of water or electrolyte drinks 

• Gentle, low-fibre foods like white rice, banana, plain chicken, or potato

• Avoiding harsh triggers like caffeine, alcohol, spicy or fatty foods (just for now)

  
  

Remember: nourishment doesn’t have to be perfect, it just needs to be enough to keep you going.

3. Make a UC Emergency Plan

Having a plan in place can ease anxiety and make decision-making easier if things escalate.

You might include:

• A list of medications you're on

• Your gastroenterologist’s contact info

• Directions to the nearest ER 

• A small hospital bag with essentials

• Someone you trust who knows what’s going on

  
  

Even writing it down in your Notes app can be enough.

4. Know Your Baselines

What’s your usual CRP? Your ferritin? Your vitamin D? Your “normal” number of bathroom trips?

Knowing your personal baseline makes it easier to recognise when things have shifted. If you're not sure what yours are, ask your doctor at your next appointment.

5. Ask for a Medication Review

If you’ve had multiple flares close together or symptoms that aren’t settling, it may be time to revisit your treatment plan.

Your doctor might suggest:

• Adjusting your dose

• Adding a new medication (like a biologic or immunosuppressant)

• Exploring lifestyle or nutrition support alongside your current plan

  
  

You don’t have to wait until you’re in crisis to ask for help. Sometimes a small tweak can make a big difference.

The Emotional Weight of Not Knowing

There’s a particular kind of stress that comes with Ulcerative Colitis, not just the physical symptoms, but the uncertainty. The wondering. The late-night spiral of “Is this bad enough to call someone?” or “Am I making a fuss over nothing?”

You’re not imagining that weight. Living with an unpredictable condition like UC means constantly assessing your own body, making decisions on the fly, and sometimes feeling like you’re walking a tightrope between “just a bad day” and “something worse.”

That takes a toll.

You might find yourself:

• Second-guessing your instincts ("What if I wait too long?")

• Feeling dismissed by others or even by doctors

• Worrying about being dramatic or overreacting

• Carrying quiet fear about long-term health, even when things seem okay

  
  

And that’s exactly why blogs like this exist: to help you name that fear and replace it with something sturdier: clarity, confidence, and calm action.

You don’t have to have all the answers. But the more you learn to trust your own awareness, the more you can step out of that anxious limbo.

If you’re feeling overwhelmed, it’s also okay to reach out to others who get it. Online communities or even a friend who knows your story can help lift the weight just a little.

FAQ’s

Can UC be life-threatening?

Rarely, but serious complications like toxic megacolon or severe bleeding can be. Acting early makes all the difference.

What are the signs of toxic megacolon?

Severe bloating, sharp belly pain, high fever, and no bowel movements. If you suspect it, go to the ER.

How much blood is too much?

If you’re passing large amounts, seeing clots, or feeling faint, it’s time to call your doctor or go in.

When should I go to the hospital?

If you have severe pain, heavy bleeding, high fever, or signs of dehydration, don’t wait. Get checked.

Is extreme fatigue dangerous?

Sometimes. If it’s sudden, overwhelming, or paired with dizziness or breathlessness, it’s worth investigating.

Final Thoughts

Ulcerative Colitis isn’t always predictable. One day, you’re coping just fine, and the next, your body throws you a symptom that makes you pause.

When that happens, here’s what I want you to remember:You are allowed to ask questions. You are allowed to get things checked. You are allowed to treat your health like it matters, because it does.

Most UC complications are manageable if caught early. The key is knowing what to watch for, trusting yourself when something feels off, and building a support system (medical and emotional) that takes you seriously.

Keep learning your body. Keep tuning in. Keep asking for help when you need it.

And if you know someone else walking this same path, send them this blog. Sometimes, the right information at the right time can change everything.