What are the causes of halitosis (bad breath)?

Causes of Halitosis (Bad Breath)

The vast majority (85-90%) of halitosis originates from oral sources, primarily bacterial breakdown of proteins on the tongue dorsum, periodontal disease, and poor oral hygiene, while only 10-20% stems from systemic conditions. 1, 2, 3

Primary Oral Causes (Most Common)

Tongue Coating and Bacterial Overgrowth

• Bacterial accumulation on the posterior third of the dorsal tongue surface is the single most dominant factor causing halitosis, even more significant than periodontal disease 2, 4, 5
• Anaerobic gram-negative bacteria degrade sulfur-containing amino acids into volatile sulfur compounds (VSCs) that produce the characteristic bad odor 2, 4

Periodontal and Gingival Disease

• Periodontal disease and gingivitis contribute significantly to halitosis through bacterial putrefaction and VSC production 1, 2, 3
• The same anaerobic bacteria implicated in periodontitis are responsible for malodor generation 4
• Look for signs of periodontal disease during evaluation, including gingival inflammation, pocket depth, and plaque accumulation 1

Dry Mouth (Xerostomia)

• Reduced salivary flow eliminates the mouth's natural cleansing mechanism, allowing bacterial proliferation and subsequent halitosis 1
• Ensuring adequate hydration and salivary flow is essential in management 1

Other Oral Factors

• Inadequate plaque control and poor oral hygiene 2, 3, 5
• Faulty dental restorations and food impaction 2, 3
• Unclean dentures or ill-fitting removable prostheses 3, 5
• Dental caries 5
• Oral carcinomas (rare but important to exclude) 3

Non-Oral/Systemic Causes (10-20% of Cases)

Upper Respiratory Tract Conditions

• Acute bacterial rhinosinusitis causes halitosis through bacterial infection and postnasal drainage 1
• Chronic rhinitis with postnasal drainage contributes when nasal discharge accumulates in the oropharynx 1
• Evaluate for nasal discharge, postnasal drip, and oropharyngeal cobblestoning during examination 1
• Tonsillitis can contribute to halitosis and may warrant tonsillectomy in children 1
• Throat infections 3

Systemic Metabolic Disorders

• Renal insufficiency or failure causes salivary disorders affecting breath odor through uremic compounds 1, 3
• Hepatic failure and pancreatic insufficiency 2, 3
• Diabetes mellitus 3
• Trimethylaminuria (fish odor syndrome) 2, 3

Gastrointestinal Factors

• Gastroesophageal reflux disease (GERD) with associated symptoms of acid reflux, heartburn, or waterbrash should be elicited in history 1
• Cases where gastric content generates oral malodor 2

Other Systemic Factors

• Moderate to heavy alcohol consumption contributes to bad breath 1
• Certain medications that reduce salivary flow 2
• Upper and lower respiratory tract infections 2

Clinical Evaluation Approach

Key History Elements

• Elicit associated symptoms including chronic throat clearing, postnasal drainage, acid reflux, heartburn, or waterbrash 1
• Screen for systemic red flags: fever, weight loss, or night sweats suggesting serious underlying disease 1
• Assess oral hygiene practices and tongue cleaning habits 5

Physical Examination Priorities

• Examine the posterior dorsal tongue surface for coating 4, 5
• Assess periodontal status and gingival health 1, 2
• Check for tonsillar hypertrophy, pharyngeal erythema, and oropharyngeal cobblestoning 1
• Evaluate nasal passages for discharge and postnasal drip 1
• Inspect dental restorations and denture fit 2, 5

Common Pitfalls to Avoid

• Do not assume halitosis is always periodontal disease—tongue coating is often the primary culprit 4, 5
• Recognize that patients with genuine halitosis often don't notice it themselves (the "bad breath paradox"), while some patients without halitosis believe they have it (pseudohalitosis or halitophobia) 6
• Don't overlook systemic causes when oral examination is unremarkable 1, 2
• Remember that dry mouth from medications or dehydration is a frequently missed reversible cause 1