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Charcoal Medicine
Those who worry about passing flatus (rectal gas) must understand that it is quite normal to do so, Drug Therapy reports. Everyone experiences this problem to a certain extent, and the amount of gas is excessive only when it causes physical discomfort or bloating of the abdomen.

Gas is produced in the colon (large intestine) by bacteria that ferment the sugars and other carbohydrates which fail to get digested and absorbed higher up in the intestinal tract. One of the  more common causes of this embarrassing problem is lactose insufficiency (milk intolerance), a condition in which certain people are incapable of digesting lactose (the natural sugar in milk) because they lack the necessary sugar-splitting enzyme, lactose.