Red or black stool: food dye or urgent?

What does red or black stool mean, and when should I worry?

Red stool is often caused by foods (beets, red dyes) or small amounts of lower-GI bleeding (like hemorrhoids), but it can also be a sign of more serious bleeding. Black stool can be caused by iron supplements or bismuth (Pepto). But black, tarry, sticky stool can signal upper-GI bleeding and needs urgent medical attention, especially with weakness, dizziness, faintness, severe pain, fever, or vomiting. If you are unsure, seek medical care.

Key takeaways

Red can be food dye, but bright red blood or clots are different. Treat them more seriously.

Iron and bismuth (Pepto) can darken stool. Black, tarry, sticky stool can be bleeding and deserves urgent care.

One-off changes can happen. Persistence + symptoms matter more than one photo.

Track Bristol type + color + timing + symptoms for a short window so you can stop guessing.

Quick answer

Red stool is often food/dye or small lower-GI bleeding (like hemorrhoids), but bright red blood or clots need more caution. Black stool can be iron or bismuth, while black, tarry, sticky stool can signal upper‑GI bleeding. This week, log exact color + Bristol type and any likely driver for 7 days.

When to seek care

Seek urgent care for black/tarry stool, large amounts of bright red blood, clots, bleeding that does not stop, faintness, severe pain, high fever, or signs of dehydration. Escalate sooner if you are on blood thinners, pregnant, immunocompromised, or have heart/kidney disease.

What to track this week

Exact color (red-tinted vs bright red blood vs black/tarry)
Bristol type + frequency + timing
Symptoms: pain, fever, vomiting, dizziness/weakness, urgency
Obvious drivers: beets/dyes, iron, bismuth (Pepto), antibiotics, alcohol
Whether the color repeats after 24 to 48 hours

A simple 7-day test

Track color + Bristol type daily for 7 days.
Note one likely driver if present (food/dye, iron, bismuth).
If the color repeats without a driver or you feel worse, seek care.

Evidence note

Color changes can be benign, but persistence plus symptoms changes urgency. This guide is for tracking, not diagnosis.

Start here: red-tinted stool vs blood

A practical distinction:

Red-tinted stool: the stool itself is colored, often due to diet or dye.
Bright red blood: visible blood in the bowl or on paper.

If you cannot tell, treat it cautiously and seek medical advice.

Red stool: common non-urgent causes

Red stool can happen after eating:

Beets
Red food dyes
Tomato skins or red sauces

If you feel well and the color resolves within 24 to 48 hours, food is a common explanation.

Red stool that needs more caution

Escalate sooner if you have:

Large amounts of bright red blood
Clots
Bleeding that doesn’t stop
Dizziness, weakness, faintness
Severe or worsening pain
Fever

Black stool: supplement effect vs a red flag

Black stool can be caused by:

Iron supplements
Bismuth, like Pepto-Bismol

But black, tarry, sticky stool can be a sign of upper-GI bleeding and needs urgent evaluation.

A simple 7-day tracking window (to stop guessing)

For a short window, keep it simple:

Color (red-tinted, bright red, or black)
Bristol type (1 to 7)
Timing and frequency
1 to 2 symptoms (pain, fever, dizziness, weakness, vomiting)
Any obvious driver (iron, bismuth, beets, dyes, antibiotics, alcohol, travel)

This makes it much easier to interpret whether you’re seeing a one-off change or a repeat pattern.

When a stool test may come up

Clinicians may consider stool tests when bleeding-like changes come with:

Persistent diarrhea
Fever
Travel or food poisoning risk
Ongoing symptoms that suggest inflammation

If you’re curious what each stool test category checks, see: Types of stool tests.

FAQs

Can beets or food dye really make stool look like blood? +

Yes. Beets, red food dyes, and some processed foods can cause red-tinted stool. The key question is whether it looks like “red-tinted stool” versus obvious bright red blood on the paper or in the bowl. If you are unsure, treat it cautiously and seek medical advice.

Can iron or Pepto make stool black? +

Yes, iron supplements and bismuth, like Pepto-Bismol, can darken stool to deep green or black. But if you are not taking these and you see black, tarry, sticky stool, treat it as possible bleeding and seek urgent care.

What does black, tarry stool mean? +

Black, tarry, sticky stool can be a sign of upper-GI bleeding, also known as melena. It deserves urgent medical evaluation, especially if you feel weak, dizzy, faint, short of breath, or have severe pain.

What are common causes of bright red blood in stool? +

Common causes include hemorrhoids and anal fissures, but infections, inflammation, and other conditions can also cause bleeding. Amount, persistence, and symptoms matter. Large amounts, clots, or worsening symptoms should be evaluated urgently.

How long should I wait if I think it’s food-related? +

Many food or dye-related changes resolve within 24 to 48 hours after the food is out of your system. If the color repeats, you feel unwell, or you can’t identify a plausible cause, consider medical advice sooner.

What should I tell a clinician? +

Share when it started, whether it’s improving or worsening, the exact color (red-tinted stool vs bright red blood vs black/tarry), stool frequency and Bristol type, recent meds (iron, bismuth, antibiotics, blood thinners), recent travel/food poisoning risk, and any symptoms (pain, fever, dizziness, weakness, vomiting).