Bad breath, or halitosis, is primarily caused by bacteria in the mouth breaking down food particles, leading to the release of foul-smelling gases. Poor oral hygiene, including infrequent brushing and flossing, allows bacteria to thrive. Dry mouth, often a result of medications or reduced saliva production, exacerbates the issue. Additionally, certain foods, such as garlic and onions, contribute to bad breath. Underlying health conditions like gum disease, respiratory infections, or digestive issues can also be culprits.