What does a white coating on the tongue indicate?

White Coating on the Tongue: Diagnostic Significance

A white coating on the tongue most commonly indicates oral thrush (candidiasis), poor oral hygiene, or benign physiologic coating, with oral thrush being the primary pathologic concern requiring treatment. 1, 2

Primary Pathologic Cause: Oral Thrush

Candida albicans is the predominant pathogen causing white coating when infectious, accounting for the majority of oral thrush cases and existing as normal flora in up to two-thirds of healthy individuals. 1, 2

Clinical Recognition of Oral Thrush

• Pseudomembranous candidiasis (classic thrush): Painless, creamy white, plaque-like lesions on buccal mucosa, oropharynx, or tongue that can be scraped off, revealing red tissue underneath 2
• White debris sprouting hyphae is characteristic of Candida infection, best visualized with microscopy 3
• Non-albicans species (C. glabrata, C. dubliniensis, C. krusei) can also cause white coating, particularly in fluconazole-resistant cases 1, 2

Key Risk Factors to Assess

Immunosuppression is the most critical risk factor:

• HIV infection, especially with CD4+ counts <200 cells/μL 1, 2
• Corticosteroid use (systemic or inhaled) 1, 2
• Malignancies, particularly hematologic cancers 2

Local factors that predispose to thrush:

• Denture use (requires both antifungal therapy and denture disinfection) 2
• Broad-spectrum antibiotic use disrupting normal bacterial flora 2
• Radiation therapy to head and neck 1

Benign Causes of White Coating

Physiologic Tongue Coating

• Normal thin white coating is common and represents accumulated oral debris and microorganisms on the papillary tongue surface 4, 5
• The dorsum of the tongue normally appears pinkish or has a thin white coating 5
• Poor oral hygiene is the strongest determinant for increased tongue coating thickness 6

Other Benign White Lesions

Verruca vulgaris (common wart):

• Caused by HPV 2 and HPV 4, presenting as well-circumscribed growth with prominent hyperkeratosis giving a white pebbly surface 3
• Uncommon in the mouth, occurs via autoinoculation from fingers 3

Oral squamous papilloma:

• Can appear white depending on degree of keratinization, caused by low-risk HPV types 6 and 11 3
• Surgical excision is recommended treatment 3

Diagnostic Algorithm

Step 1: Attempt to Scrape the White Coating

• If it scrapes off easily revealing red tissue: Strongly suggests oral thrush 2
• If it does not scrape off: Consider other diagnoses like leukoplakia, lichen planus, or HPV-related lesions 3

Step 2: Assess Risk Factors

• Review immune status, medication history (steroids, antibiotics), denture use, and oral hygiene practices 1, 2
• In elderly long-term care residents, 84% are colonized with yeast, making them particularly vulnerable 2

Step 3: Consider Associated Symptoms

• Thirst and gastrointestinal symptoms may accompany pathologic tongue coating 7
• Halitosis is commonly associated with tongue coating but does not distinguish between benign and pathologic causes 4, 6

Step 4: If Diagnosis Uncertain After 2 Weeks

• Perform biopsy if lesion persists beyond 2 weeks without improvement 3
• Consider referral to oral medicine specialist or otolaryngologist 3

Critical Pitfalls to Avoid

• Do not dismiss white coating in immunocompromised patients: Oral thrush may spread to esophagus causing dysphagia and chest pain 2
• Do not confuse with angular cheilitis: This presents as inflammation at mouth corners, often requiring combination antifungal-corticosteroid therapy 8
• Smoking and denture use also correlate with increased tongue coating, though less strongly than oral hygiene 6
• Yellow or black discoloration suggests different pathology (bacterial overgrowth or "black hairy tongue") and requires different evaluation 7, 9