The sudden appearance of red or reddish stool can be startling, prompting immediate concern about internal bleeding. This alarm is often unnecessary, as the most frequent cause of temporary red stool is something consumed recently. A large bowl of tomato soup, or other products derived from tomatoes, can indeed make stool appear red. This color change is usually a harmless side effect of the food’s natural coloring passing through the digestive system. Understanding the difference between a dietary color change and a medical indicator is important for peace of mind.
How Food Pigments Affect Stool Color
The normal brown color of stool is a result of the breakdown of old red blood cells. The liver processes hemoglobin into bilirubin, which bacteria chemically transform into stercobilin, the compound that creates the characteristic brown hue.
The red color from tomatoes comes from lycopene, a carotenoid plant compound. Lycopene is a robust pigment that digestive enzymes do not fully break down or metabolize. Because it resists complete absorption, a significant amount of the red pigment remains intact as it passes through the intestines.
When a substantial quantity of a lycopene-rich food, such as tomato soup, is eaten, the undigested red pigment mixes with the stool mass. This process overwhelms the natural brown color, resulting in a distinctly reddish or pinkish-red bowel movement. This color shift is purely cosmetic and confirms the pigment’s stability throughout the digestive tract.
Other Dietary Sources of Red Stool
Tomato products are not the only food items that can lead to discoloration. Other deeply pigmented foods contain compounds that similarly escape full digestive processing. Beets are a common culprit, containing a powerful pigment called betanin that can turn stool pink or red. The intensity of this effect depends on the amount consumed and individual digestive differences.
Artificial colorings are also highly stable and can significantly change stool color. The synthetic dye Red 40, frequently found in red velvet cake, icing, drink mixes, and certain candies, is often excreted without being chemically altered. Consuming large amounts of these artificially colored items can lead to bright red or dark-colored stools.
Other natural foods, such as cranberries or red peppers, also contain pigments that resist digestion. You may observe small, undigested red fragments of food, like tomato skin or pepper pieces, mixed into the stool. These dietary changes are temporary, and the stool color should return to its normal brown within a day or two.
When Red Stool Signals a Health Issue
While dietary causes are the most common explanation for red stool, it is important to know when the color signals a medical problem. Red stool caused by blood is referred to as hematochezia and originates primarily from the lower gastrointestinal tract. This blood is usually bright red because it has not been exposed to digestive enzymes for long.
Common causes of bright red blood include hemorrhoids or small tears in the anal lining called anal fissures. Conditions like diverticulosis, inflammatory bowel disease, or polyps in the colon can also cause lower GI bleeding. If the red color persists past a few bowel movements, or if the red color is clearly blood and not just mixed pigment, medical attention is necessary.
A different and more concerning presentation is a very dark, black, and tarry stool, known as melena. Melena indicates bleeding higher up in the digestive tract, such as the stomach or upper small intestine. The blood turns black because stomach acid and digestive enzymes have broken down the hemoglobin. If red stool is accompanied by symptoms like severe abdominal pain, weakness, lightheadedness, or dizziness, contacting a healthcare provider is prudent to determine the underlying cause.