White stool is caused by lack of bile, the digestive fluid produced by the liver and stored in the gallbladder. Causes of occasionally white stool range from reactions to medications to serious medical conditions such as hepatitis or cancer, and people who experience it should consult their physician.

Medications

Over-the-counter anti-diarrheal medications containing bismuth subslicylate, including Kaopectate and Pepto-Bismol, can cause white stool in if taken large doses, according to the Mayo Clinic. Some prescription medications, including some antibiotics and antifungal drugs, can cause occasionally white stool.

Liver Infections or Disease

Liver infections such as hepatitis can cause the liver to produce too little bile, leading to white stool. Biliary cirrhosis, an autoimmune disease in which the bile ducts in the liver are slowly destroyed, also can lead to white stool. In both cases, occasional white stool becomes more frequent as the disease progresses.

Gallstones

Gallstones can cause white stool by blocking the main bile duct, preventing bile made by the liver from reaching the intestines. Gallstones often cause intermittent but severe pain in the upper middle or right side of the upper abdomen.

Malabsorption

Malabsorption disorders such as Celiac disease (an autoimmune reaction to the protein gluten that destroys the intestinal villa) can cause occasionally white stool. In this case, correcting the malabsorption--which can be caused by food intolerances or more serious conditions such as cancer--should fix the stool color.

Cancer

Sometimes, white stool can be caused by cancer of the biliary duct (gallbladder and bile duct), liver cancer, pancreatic cancer or lymphoma. The Mayo Clinic notes that any white stool, even if infrequent, isn't normal and should be evaluated by a doctor.

Source:

Mayo Clinic: White Stool

Jackson-Siegelbaum Gastroenterology: Gallstones