Trench mouth is an infection that affects the mouth and throat. The condition is also known by the terms Vincent's infection and necrotizing ulcerative gingivitis. It was given the name trench mouth during World War I (1914-1918), when thousands of soldiers got it while fighting in the trenches. The infection is caused by bacteria that are normally present in small numbers in everyone's mouth. Most cases of trench mouth occur when such factors as stress, poor nutrition, or smoking disrupt the mouth's environment and these bacteria multiply.