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Change in bowel habits lasting weeks, or thin stools

Also called: Bowel habit change, pencil-thin stools

A change in bowel habits lasting more than a few weeks, or thin stools, should be checked, especially after age 45. Most causes are harmless, but it can be a sign of colon cancer.

Common causesIBS, diet, medicines, colon cancer
Usually serious?Can be
Get checked ifLasts weeks, or with bleeding
If you think it's an emergency, call 911.Thinking about suicide? Call or text 988.

Overview

Changes can include diarrhea, constipation, or thinner stools.

Blood, weight loss, or tiredness need attention.

When to get medical care

Call 911Heavy bleeding.
Get care todayBlack stools. Severe belly pain.
See a doctor soonChanges lasting more than 3 weeks.

Causes

Causes include IBS, diet, medicines, infections, IBD, and colon cancer.

OwieClear has pages on 4 conditions that can cause change in bowel habits lasting weeks, or thin stools. Each shows how soon to get care.

Common causes

Less likely causes

  • Appendix cancerSee a doctor if it doesn't get better

    A rare cancer of the appendix.

  • Primary peritoneal cancerSee a doctor if it doesn't get better

    Cancer of the thin lining of the belly (peritoneum) that acts like ovarian cancer.

What you can do at home

  • Eat fiber.

Medicines

Depends on cause.

At the doctor

A colonoscopy may be needed.

Questions you may be asked

  • Changes
  • Bleeding
  • Family history

The exam

A belly exam.

Tests

  • Colonoscopy
  • Blood tests

Prevention

Get screened.

  • Start colon screening at 45

Check your symptoms

Most symptoms have more than one possible cause. The symptom checker looks at all of your symptoms together, plus your age, and shows how soon to get care.

Start the symptom checker

Sources

Last updated 2026-11-13.