Don't ignore diarrhea that has gone on for weeks.

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Sometimes diarrhea goes on ... for weeks. That's when a more serious problem is probably responsible. Your doctor can ferret out the cause. See a doctor for your diarrhea if:

  • You see blood in your stool.
  • You experience symptoms of dehydration, including dizziness when you stand up, scanty and deep-yellow urine, increased thirst, and dry skin. Children may also cry without producing tears.
  • You've got a fever or shaking chills.
  • Your diarrhea persists for more than 48 to 72 hours.
  • The person with diarrhea is very young, very old, or chronically ill.

Lactose intolerance. If you get diarrhea after drinking milk, your body may have lost some or all of its ability to digest lactose, the sugar in milk and dairy products. Lactose intolerance is the most common cause of chronic diarrhea. If you can't drink milk, take calcium supplements or drink calcium-fortified juice or soy milk.

Celiac disease. In this case, you can't digest gluten, which is part of wheat.

Irritable bowel syndrome (IBS). Some people with IBS have constipation and some have diarrhea. Others alternate between the two.

Parasitic infections. These can hang on indefinitely.

Crohn's disease or ulcerative colitis. These two conditions are similar, and no one knows their cause. But the end results are inflammation of the bowel and diarrhea, often accompanied by pain.

Systemic illnesses. Chronic diarrhea can be a complication of diseases such as diabetes, scleroderma, and hyperthyroidism.

Cancer. The cause of diarrhea is usually more benign, but one of the warning signs of tumors in the bowel is diarrhea, especially if blood is present.