Quick answer: A change in bowel habits needs a doctor when it lasts more than a few weeks without an obvious cause, or when it comes with blood in or on your poop, black or tarry stools, weight loss you can't explain, ongoing belly pain, fever, vomiting, or symptoms that wake you at night. Short-lived changes after travel, illness, a new medicine or a diet shift are common and can usually be tracked for a week or two first.
A change in bowel habits means your usual pattern shifts: you go more or less often, your poop gets looser or harder, or it feels different to pass. Most changes are temporary. Some are the body's way of flagging something that needs a proper look.
The hard part is telling them apart, and most pages either scare you or shrug. This guide sorts changes by urgency, using what US and UK clinical guidelines actually say, and shows what to write down so the conversation with your doctor is faster.
Key takeaways
- "Normal" is wide: healthy adults range from about three bowel movements a week to three a day [11]. What matters is a change from your normal.
- Blood, black stools, unexplained weight loss, fever, persistent vomiting, constant belly pain or being unable to pass gas need prompt care, not a wait-and-see diary [1][2][3].
- A change with no clear cause that lasts more than about three weeks is a reason to book an appointment, even if it feels mild [3][4].
- Screening and symptoms are different: US guidelines start routine colorectal screening at 45 for people without symptoms [8][9]. If you have symptoms, you need an evaluation at any age.
- For changes that aren't red flags, a 1–2 week log of stool type, frequency and symptoms makes the appointment more useful.
What counts as a change in bowel habits?
A change in bowel habits is any lasting shift from your personal baseline in how often you go, what your stool looks like, or how it feels to pass. Doctors care about the change more than any single number, because healthy people vary so much.
In a Swedish population study that screened out gut disease with colonoscopy and lab tests, normal stool frequency ranged from three per week to three per day, and some urgency, straining and a feeling of incomplete emptying were common even in healthy people [11]. So going every other day isn't a problem if that has always been you. Going every other day when you used to go twice daily is worth noticing.
Changes clinicians ask about include:
| Change | What it looks like | Plain-language example |
|---|---|---|
| Frequency | More or fewer bowel movements than your usual | "I used to go once a day; now it's 4–5 times." |
| Consistency | Shift on the Bristol Stool Scale (type 1 hard lumps to type 7 watery) | "Mostly type 4 before, mostly type 6 for three weeks." |
| Shape or size | Narrower stools than usual [7] | "Thinner than normal, most days." |
| Passage | Urgency, straining, feeling you haven't finished [3][7] | "I keep feeling I need to go right after I've been." |
| Colour | Black, maroon, red streaks, very pale | "Black and sticky twice this week." |
| Timing | New symptoms at night | "I wake up needing to go." |
If you're not sure how to put your own change into words, our guide on how to describe your poop to a doctor has a ready-made script.
Which symptoms mean go now, not later?
Some signs should not go into a tracking diary first. They need same-day care or emergency care, regardless of how long they have lasted.
Call 911 or go to the emergency room
- Heavy bleeding from your bottom that won't stop, or a lot of blood or large clots when you poop [3]
- Black or bloody stool with dizziness, fainting, confusion, a racing heart, or vomiting blood [12]
- Severe belly pain with vomiting and being unable to pass stool or gas, which can signal a blockage [1][3]
- Signs of severe dehydration with diarrhea, such as confusion or very little urine [2]
Get a same-day or urgent appointment
The NHS advises urgent help (an urgent GP appointment or NHS 111 in the UK) for poop that is black or dark red, or bloody diarrhea [3]. NIDDK, part of the US National Institutes of Health, lists these as reasons for adults to talk with a doctor right away [1][2]:
| With constipation | With diarrhea |
|---|---|
| Bleeding from the rectum or blood in the stool | Diarrhea lasting more than 2 days |
| Constant pain in your abdomen | High fever |
| Inability to pass gas | Six or more loose stools in a day |
| Vomiting | Severe pain in the abdomen or rectum |
| Fever | Black, tarry stools, or stools with blood or pus |
| Lower back pain | Frequent vomiting or signs of dehydration |
| Losing weight without trying | A change in mental state |
A note on black stool: iron tablets, bismuth products such as Pepto-Bismol, black licorice and blueberries can darken poop [12]. If you can't link it to one of those, treat black, tarry stool as possible bleeding higher in the gut and get checked promptly [12]. Our poop color chart covers the harmless colors too.
Don't assume blood is "just hemorrhoids"
Hemorrhoids are a common cause of bright red blood. But rectal bleeding was the strongest of four warning signs linked to colorectal cancer in younger adults in a large US study, alongside abdominal pain, diarrhea and iron-deficiency anemia [10]. Doctors themselves list blood as a reason to be examined rather than self-diagnosed [7]. Let a clinician decide it's hemorrhoids.
How long should a change last before you see a doctor?
If there's no red flag and no obvious cause, book an appointment when a change has lasted about three weeks, or sooner if it's getting worse. Here's where that number comes from, and why you'll see different numbers online.
- UK: NHS and cancer charities commonly use three weeks as the point to see a GP about an unexplained change in bowel habit. The NHS symptoms page itself simply says to see a GP if you have any of the listed symptoms [3]. NICE now tells GPs to offer a stool test for hidden blood (FIT) to any adult with a change in bowel habit, with no age cutoff [4].
- US: The American Cancer Society lists changes in bowel habits "lasting more than a few days" among colorectal cancer symptoms, and advises seeing a doctor so the cause can be found [7]. NIDDK says to see a doctor for constipation that doesn't improve with self-care [1], and for adult diarrhea that lasts more than 2 days [2].
- IBS framework: Doctors usually think about irritable bowel syndrome (IBS) after symptoms have been around for months. NICE suggests assessing for IBS after six months of pain, bloating or bowel change [5], but only after checking for red flags first [5][6].
The practical takeaway: two to three weeks of an unexplained change is long enough to book. Use that time to keep a simple log, so you arrive with facts rather than impressions. Specialist waits can be long, so if you need a gastroenterologist, our guide to the GI appointment wait time covers what to do in the meantime.
Does age matter? Screening vs symptoms
Age changes the odds, not the rule. A new, unexplained change needs a look at any age. Age mainly affects how quickly doctors move to tests such as a colonoscopy.
"Older age at onset" is a warning sign. The American College of Gastroenterology (ACG) lists older age at symptom onset as an alarm feature, along with blood in the stool, black stool, unintentional weight loss, and a family history of inflammatory bowel disease (IBD), colon cancer or other significant GI disease [6]. The ACG doesn't attach a single age to "older". NICE's referral rules use specific ages: they offer FIT to adults 50 and over with unexplained rectal bleeding, abdominal pain or weight loss, to those 40 and over with unexplained weight loss plus abdominal pain, and to those 60 and over with anemia [4]. So if your symptoms started for the first time in your 50s or later, mention that clearly.
Younger doesn't mean "too young." In the US study mentioned above, about 5,000 people diagnosed with colorectal cancer before 50 were compared with about 22,000 people without it. Rectal bleeding, abdominal pain, diarrhea and iron-deficiency anemia in the 3 months to 2 years before diagnosis were all linked to higher risk, with rectal bleeding the strongest (odds ratio 5.13) [10]. These symptoms are still far more often caused by something benign. Persistent ones deserve a proper workup, though, whatever your age.
Screening is for people without symptoms. The American Cancer Society reaffirmed in May 2026 that people at average risk should start colorectal cancer screening at 45 and continue through 75 [8]. The US Preventive Services Task Force also recommends screening from 45. Its recommendation explicitly applies to adults without symptoms [9]. That distinction matters:
| Your situation | What to ask for |
|---|---|
| 45 or older, no symptoms, average risk | Routine screening. Ask which test suits you (stool-based or visual exam) [8] |
| Any age, with a new, persistent change or red-flag symptom | A diagnostic evaluation, not a home screening kit. Tell the doctor about your symptoms. |
| Family history of colorectal cancer, IBD or a known genetic syndrome | Ask whether you need to start screening earlier or more often [8][9] |
| You had a positive stool or blood screening test | Follow-up colonoscopy, ideally within 6 months [8] |
If you have symptoms, don't use a negative home screening test as reassurance. NICE notes that even a low FIT result shouldn't delay referral when symptoms remain concerning [4].
Which changes can you track first?
Changes with an obvious, temporary trigger and no red flags can usually be watched for one to two weeks. Common examples:
- Travel, jet lag or a change in routine
- A stomach bug that is improving (keep an eye on fluids)
- A new medication or supplement. Iron tablets, for example, can darken stool [12]. Ask your pharmacist whether gut side effects are expected.
- A big diet shift, such as more fiber, a new diet or more coffee or alcohol
- Stress, poor sleep or your menstrual cycle
Even then, set a review date. If things haven't settled by then, or a red flag appears, stop tracking and book the appointment. NIDDK also advises seeing a doctor if constipation doesn't respond to self-care, or if you have a family history of colon or rectal cancer [1].
The decision table
Use this table as a rough sort, not a diagnosis. When in doubt, call your doctor's office or a nurse line and describe what's happening.
| What you notice | Action | Timeframe |
|---|---|---|
| Heavy or non-stop rectal bleeding, black stool with dizziness, vomiting blood, severe pain with no gas or stool | Emergency care | Now |
| Black/tarry or maroon stool, bloody diarrhea, high fever, 6+ loose stools a day, signs of dehydration | Urgent same-day care | Today |
| Any blood in or on stool, unexplained weight loss, constant belly pain, symptoms waking you at night | Book an appointment, and say these words when you call | Within days |
| Unexplained change in frequency, consistency or shape lasting about 3 weeks | Book a routine appointment; bring a log | Within 2–3 weeks |
| New change with an obvious trigger (travel, new medicine, diet change), no red flags | Track it and set a review date | 1–2 weeks |
| Long-standing pattern that hasn't changed and has been checked before | Track to spot triggers; mention it at your next visit | Ongoing |
How to track a bowel change before your appointment
The aim is a short, honest record that answers the questions your doctor will ask: what changed, when it started, how often it happens and what comes with it. A symptom diary is also more accurate than memory. In one study of 100 patients, recalled stool consistency agreed with a one-week diary only 12.5% of the time [13] (our guide to keeping a symptom diary your doctor will use covers this).
What to record each time you go:
- Date and time
- Bristol type (1–7)
- Anything unusual: blood, mucus, black or pale color, urgency, straining, accidents
- Belly pain or bloating, rated 0–10
- Notes: new medicines, travel, illness, period, stress
Once a day: what you ate (roughly), any missed days with no bowel movement, and whether symptoms woke you up.
An illustrative week (example data, not a real patient):
| Day | BMs | Bristol types | Pain (0–10) | Flags | Notes |
|---|---|---|---|---|---|
| Mon | 3 | 6, 6, 5 | 3 | Urgency | Started new iron tablet last week |
| Tue | 4 | 6, 6, 7, 6 | 4 | Woke at 3am to go | — |
| Wed | 3 | 6, 5, 6 | 3 | — | — |
| Thu | 4 | 7, 6, 6, 6 | 5 | Woke at night | Weight down 1.5 kg since last month |
| Fri | 3 | 6, 6, 5 | 3 | — | — |
In this example, the night-time symptoms and weight loss are what move it from "track" to "book an appointment soon". The log makes that obvious in seconds.
If you use an app, inspect the actual record you plan to share and ask your practice which format it accepts. The Get Regular App tour and Doctor Report explanation describe the intended workflow; check current availability and the file itself before relying on it for a visit.
When to see a doctor
To recap the red flags. See a doctor promptly, or get emergency care where noted above, if you have:
- Blood in or on your stool, or bleeding from your bottom
- Black, tarry or maroon stools that you can't explain by iron, bismuth or food
- Unintentional weight loss
- Persistent fever
- Symptoms that wake you from sleep
- Severe or constant belly pain, or a lump in your belly
- Vomiting, or being unable to pass gas or stool
- Signs of anemia: unusual tiredness, breathlessness, or low iron on a blood test
- A first-ever change in bowel habits later in life
- A family history of colorectal cancer, IBD or celiac disease
- Any change from your normal that lasts more than about three weeks
FAQ
Is a change in bowel habits always serious? No. Most changes come from diet, infections, medicines, stress or travel, and settle within days. The ones to act on persist, keep getting worse, or come with red flags such as blood, weight loss or night-time symptoms [3][7].
When should I see a doctor for constipation? See a doctor if constipation doesn't improve with self-care, or if you have a family history of colon or rectal cancer. Go right away if it comes with rectal bleeding, constant belly pain, being unable to pass gas, vomiting, fever, lower back pain or weight loss [1].
When should I see a doctor for diarrhea? NIDDK advises adults to see a doctor for diarrhea lasting more than 2 days, a high fever, six or more loose stools a day, severe pain, black or bloody stools, or signs of dehydration [2]. People who are pregnant, over 65, on antibiotics or immunocompromised should keep in touch with their doctor sooner [2].
Can I use a home stool test instead of seeing a doctor? Not if you have symptoms. Home stool tests are screening tools for people without symptoms [9]. With symptoms, a doctor needs to evaluate you, and NICE notes that a negative stool test shouldn't delay referral if concern remains [4].
I'm under 45. Should I still worry about blood in my stool? Yes, get it checked. Most causes are benign, but rectal bleeding was the strongest warning sign for colorectal cancer in younger adults in a large US study [10]. A doctor can examine you and decide what tests, if any, you need.
Sources
- NIDDK. Symptoms & Causes of Constipation. https://www.niddk.nih.gov/health-information/digestive-diseases/constipation/symptoms-causes
- NIDDK. Symptoms & Causes of Diarrhea. https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/symptoms-causes
- NHS. Bowel cancer: Symptoms. https://www.nhs.uk/conditions/bowel-cancer/symptoms/
- NICE. Suspected cancer: recognition and referral (NG12), recommendations 1.3.1–1.3.5 (last updated 15 April 2026). https://www.nice.org.uk/guidance/ng12/chapter/recommendations-organised-by-site-of-cancer
- NICE. Irritable bowel syndrome in adults: diagnosis and management (CG61). https://www.nice.org.uk/guidance/cg61/chapter/Recommendations
- Lacy BE, et al. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol 2021;116:17-44. https://journals.lww.com/ajg/Fulltext/2021/01000/ACG_Clinical_Guideline__Management_of_Irritable.11.aspx
- American Cancer Society. Colorectal Cancer Signs and Symptoms. https://www.cancer.org/cancer/types/colon-rectal-cancer/detection-diagnosis-staging/signs-and-symptoms.html
- American Cancer Society. American Cancer Society Updates Colorectal Cancer Screening Guideline (27 May 2026). https://pressroom.cancer.org/colorectal-cancer-screening-guideline-update-2026
- US Preventive Services Task Force. Colorectal Cancer: Screening (2021). https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/colorectal-cancer-screening
- Fritz CDL, et al. Red-flag signs and symptoms for earlier diagnosis of early-onset colorectal cancer. J Natl Cancer Inst 2023;115(8):909-916. https://academic.oup.com/jnci/article/115/8/909/7147891
- Walter SA, et al. Assessment of normal bowel habits in the general adult population: the Popcol study. Scand J Gastroenterol 2010;45(5):556-66. https://doi.org/10.3109/00365520903551332
- MedlinePlus. Stools - black or tarry. https://medlineplus.gov/ency/article/003130.htm
- Hudgi A, et al. Accuracy of patient-reported bowel symptoms for fecal incontinence: Historical recall versus prospective evaluation. Neurogastroenterol Motil 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC10842103/
This article is for general education and isn't medical advice. Get Regular is a tracking app — it doesn't diagnose or treat any condition. If you have red-flag symptoms or ongoing changes in your digestion, talk to a doctor.