Symptoms of Crohn's Disease: Early Signs and Flares

What are the most common symptoms of Crohn's disease?

Crohn's disease causes inflammation that penetrates deeply into all layers of the bowel wall — unlike ulcerative colitis, which stays on the mucosal surface. This transmural inflammation explains many of its characteristic symptoms and complications 1Ref 1Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE (2018).ACG Clinical Guideline: Management of Crohn's Disease in Adults.Crohn's disease symptom clusters, extraintestinal manifestations, flare characteristics, distinction from UC, and diagnostic approach including endoscopy, imaging, and biomarkers..

Persistent diarrhea — often loose, frequent, and urgent — is the hallmark GI symptom. It may or may not contain blood, depending on which part of the GI tract is affected.

Abdominal pain and cramping — frequently in the right lower abdomen, where the small intestine meets the colon (the ileocecal region), though pain location depends on which segment is inflamed.

Fatigue — disproportionate to other findings and often underestimated. Chronic systemic inflammation is energy-consuming, and nutritional deficiencies from malabsorption compound this.

Unintentional weight loss — from reduced appetite, malabsorption, and the metabolic demands of ongoing inflammation.

Reduced appetite and nausea, particularly during flares.

Symptoms tend to come and go: periods of active disease (flares) alternate with periods of remission in which symptoms improve or resolve. The unpredictability of this pattern is one of the most disruptive aspects of Crohn's 2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2023).Crohn's Disease.Patient-education overview of Crohn's disease symptoms, remission, flare triggers, and disease course..

What does a Crohn's flare feel like?

During a flare, previously manageable symptoms can intensify significantly. Common experiences include:

• Waking at night with diarrhea or cramping
• An urgent, difficult-to-control need to use the bathroom
• Visible blood in stool (more common when the colon is involved)
• Increased abdominal pain that may become constant rather than intermittent
• Low-grade fever and a sense of being systemically unwell
• Intensified fatigue and difficulty functioning normally

Flares can be triggered by stress, infections, certain foods, or stopping medications, or can occur without an obvious precipitating event 2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2023).Crohn's Disease.Patient-education overview of Crohn's disease symptoms, remission, flare triggers, and disease course..

Early signs of Crohn's disease that are easy to miss

Crohn's often takes months or even years to diagnose because early symptoms can be nonspecific:

Recurrent mouth sores (aphthous ulcers): Crohn's can affect the mouth; unusually frequent or slow-healing canker sores can be an early signal 1Ref 1Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE (2018).ACG Clinical Guideline: Management of Crohn's Disease in Adults.Crohn's disease symptom clusters, extraintestinal manifestations, flare characteristics, distinction from UC, and diagnostic approach including endoscopy, imaging, and biomarkers..

Perianal symptoms: Fissures, skin tags, or abscesses around the anus can precede intestinal symptoms in some people and are often initially attributed to other causes.

Joint aches: Peripheral arthritis (ankles, knees, wrists) and, less commonly, spine involvement are recognized extraintestinal manifestations that can appear alongside or before GI symptoms 1Ref 1Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE (2018).ACG Clinical Guideline: Management of Crohn's Disease in Adults.Crohn's disease symptom clusters, extraintestinal manifestations, flare characteristics, distinction from UC, and diagnostic approach including endoscopy, imaging, and biomarkers..

Eye inflammation: Uveitis and episcleritis are less common but well-documented manifestations.

Skin changes: Erythema nodosum (tender red nodules on the shins) and pyoderma gangrenosum (painful skin ulcers) are associated with active Crohn's.

Iron deficiency anemia: Chronic low-grade GI bleeding or impaired iron absorption can produce anemia, sometimes identified on routine blood work before a GI diagnosis is made.

How is Crohn's disease different from ulcerative colitis?

Both are forms of inflammatory bowel disease (IBD), but they have important differences that shape treatment 1Ref 1Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE (2018).ACG Clinical Guideline: Management of Crohn's Disease in Adults.Crohn's disease symptom clusters, extraintestinal manifestations, flare characteristics, distinction from UC, and diagnostic approach including endoscopy, imaging, and biomarkers.:

The distinction matters for treatment selection and risk assessment. Endoscopy with biopsy is required to distinguish the two reliably.

How is Crohn's disease diagnosed?

There is no single blood test that diagnoses Crohn's. A gastroenterologist uses a combination of approaches 1Ref 1Lichtenstein GR, Loftus EV, Isaacs KL, Regueiro MD, Gerson LB, Sands BE (2018).ACG Clinical Guideline: Management of Crohn's Disease in Adults.Crohn's disease symptom clusters, extraintestinal manifestations, flare characteristics, distinction from UC, and diagnostic approach including endoscopy, imaging, and biomarkers.:

Blood tests: May reveal elevated inflammatory markers (CRP, ESR), anemia, elevated white cell count, or nutritional deficiencies.

Stool tests: Fecal calprotectin — a protein released by white blood cells in an inflamed bowel — is elevated in active IBD. A 2023 systematic review and meta-analysis found pooled sensitivity of 81% and specificity of 74% for distinguishing endoscopically active Crohn's from inactive disease 3Ref 3Bohra A, Mohamed G, Vasudevan A, Lewis D, Van Langenberg DR, Segal JP (2023).The Utility of Faecal Calprotectin, Lactoferrin and Other Faecal Biomarkers in Discriminating Endoscopic Activity in Crohn's Disease: A Systematic Review and Meta-Analysis.Fecal calprotectin as a validated biomarker for distinguishing active IBD from functional GI disorders such as IBS, with pooled sensitivity 81% and specificity 74% for endoscopic Crohn's activity., and it helps differentiate inflammatory bowel disease from IBS, in which no inflammation is present.

Colonoscopy with biopsy: The key diagnostic procedure. Allows direct visualization of the colon and terminal ileum, with tissue biopsy confirming the histological pattern of Crohn's inflammation.

Imaging: CT or MRI enterography helps evaluate small bowel disease extent, strictures, fistulas, and other complications that endoscopy cannot reach.

Diagnosis typically requires more than one of these approaches, which is why early referral to a gastroenterologist — rather than waiting years — improves outcomes.

When should you see a gastroenterologist?

See a gastroenterologist promptly if you have:

• Diarrhea that has lasted more than four weeks without a clear cause
• Recurrent episodes of abdominal pain and diarrhea over months
• Blood in stool combined with abdominal pain or weight loss
• Unintentional weight loss alongside GI symptoms
• A family history of IBD with new GI symptoms
• GI symptoms alongside joint pain, eye inflammation, or unexplained skin findings

Gale does not provide gastroenterology directly, but a Gale primary care clinician can begin your initial evaluation — ordering inflammatory markers and a fecal calprotectin — and coordinate a prompt GI referral when the picture warrants it.