There are a few reasons why you may have bad breath while traveling. Bad breath can happen while traveling, when your salivary glands slow down the production of saliva, which allows bacteria to grow inside the mouth and bad breath to develop. Often times travelers alter their food intake while at the airport and on the plane.
Either by increasing their fast food and soda intake which can leave food particles in the mouth that produce a sulfur compound and cause bad breath, or by fasting which still cause bad breath by bringing back morning breath.
In addition to food changes, travelers often fail to maintain their dental hygiene habits causing bad breath by forgetting to brush and floss daily.