2 Answers

Gluten is a type of protein found in most grains, cereals and bread.  People with celiac disease cannot eat gluten.

Gluten is something found in barley, oat, wheat, rye.  It is also found as a thickening agent (modified something or other starch).

Gluten intolerance can cause a number of problems.....headaches, hair loss, breathing difficulties, indigestion and reflux are just a few

My sister was recently diagnosed as being gluten intolerant.  She immediately cut all gluten from her diet and ALL of her symptoms have disappeared, practically overnight.. 

Note:  She was told that she should have her own jar of mayonnaise.  Even a crumb of bread that has gluten in it (wheat, white, among others) that might get in the mayo jar from "double-dipping" could produce symptoms.  JUST A CRUMB can taint the whole jar.