What causes oral thrush?

Causes of Oral Thrush

Oral thrush is primarily caused by an overgrowth of Candida species, most commonly Candida albicans, in the oral cavity due to various local and systemic factors that disrupt the normal oral microbiome and host immune defenses. 1

Primary Causative Organisms

• Candida albicans is the predominant pathogen causing oral thrush, found in the oral cavity of up to two-thirds of healthy individuals as part of normal flora 1
• Other Candida species may also cause oral thrush, including C. glabrata, C. tropicalis, C. dubliniensis, and C. krusei, particularly in cases of refractory disease 1, 2

Local Factors Contributing to Oral Thrush

• Denture use is a significant risk factor, with denture-related candidiasis requiring both antifungal therapy and proper denture disinfection 1, 3
• Poor oral hygiene allows for increased colonization and overgrowth of Candida species 2, 3
• Impaired salivary gland function (hyposalivation) reduces the natural cleansing and antimicrobial properties of saliva 2, 3
• Broad-spectrum antibiotic use disrupts the normal bacterial flora that typically compete with and inhibit Candida overgrowth 1, 2
• Local tissue damage from radiation therapy for head and neck cancers creates an environment favorable for Candida colonization 2

Systemic Factors Contributing to Oral Thrush

• Immunosuppression is a major risk factor, particularly:

  • HIV infection, especially with CD4 counts <200 cells/μL 1
  • Diabetes mellitus, which impairs neutrophil function and increases glucose in saliva 2, 3
  • Malignancies, particularly leukemia and other hematologic cancers 1, 2
  • Steroid use, both systemic and inhaled corticosteroids 1
  • Immunosuppressive therapy for organ transplantation or autoimmune conditions 4, 2

• Nutritional deficiencies and malnutrition can compromise immune function and mucosal integrity 2, 3

Clinical Presentations and Recognition

• Pseudomembranous candidiasis (classic thrush): characterized by painless, creamy white, plaque-like lesions on the buccal mucosa, oropharynx, or tongue that can be scraped off 1
• Erythematous candidiasis: presents as red patches without white plaques, typically on the palate or tongue 1
• Angular cheilitis: inflammation at the corners of the mouth, often associated with Candida infection 1, 3

Complications and Concerns

• In immunocompromised patients, oral thrush may spread to the esophagus (esophageal candidiasis) causing odynophagia, retrosternal pain, and difficulty swallowing 1
• Persistent and refractory oral thrush may indicate underlying undiagnosed immunodeficiency or the development of drug-resistant Candida strains 4, 2
• In severely immunocompromised patients, there is risk of dissemination to distant organs 2

Prevention Strategies

• For HIV-infected patients, antiretroviral therapy is strongly recommended to reduce the incidence of recurrent infections 1
• For denture wearers, proper denture hygiene including daily disinfection and removing dentures at night is essential 1, 3
• Maintaining good oral hygiene and regular dental check-ups 3
• Addressing underlying medical conditions that contribute to immunosuppression 1

Understanding these various factors that cause oral thrush is crucial for effective management and prevention of recurrent infections, particularly in vulnerable populations.