Gas - a social problem with physical roots.

Although a frequenty joked-about condition, flatulence - commonly referred to as "gas" - can be a serious matter with embarrassing social repercussions. While there are many causes of flatulence, in some cases, it is unknown.

Everyone produces gas every day, beginning just a few days after birth. This condition occurs when a person has a build@up of flatus, or intestinal gas formed by swallowed air, sometimes accompanied by abdominal discomfort, which is relieved by the passage of flatus. Gas occurs more often when individuals are in a prone position; when they stand, most swallowed air passes back up the esophagus, to be expelled through the mouth.

Many people are less able to control flatulence. As they grow older, they pass gas more frequenty. This may be due to weakened pelvic muscles, which control the process of holding or passing gas. Previous pregnancies or abdominal surgery may weaken pelvic muscles and make control more difficult.

The normal amount of flatus a person passes on an average day is 400-2,000 milliliters - between a pint and a half-qallon. The amount varies from person to person and in the same person, depending upon diet. Gas is formed in the large intestine as a result of the action of bacteria on carbohydrates and amino acids in digested food. It consists of hydrogen, carbon dioxide, nitrogen, oxygen, and methane.

A main cause of gas build-up is aerophagia, or air swallowing, due to rapid gulping of foods and liquids, gum-chewing, and even...