What causes aphthous ulcers (canker sores)?

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From the Guidelines

Aphthous ulcers, also known as canker sores, are primarily caused by a combination of local and systemic factors, including traumatic, infectious, allergic factors, and may be associated with skin disease, autoimmune disease, tumor, inflammatory bowel disease, and so on, although the exact cause is often unknown 1. The etiology of aphthous ulcers is complex and diverse, and can be attributed to various factors such as:

  • Traumatic factors, including mechanical, physical, or chemical stimuli
  • Infectious factors
  • Allergic factors
  • Systemic diseases, such as inflammatory bowel disease, autoimmune disease, or skin disease
  • Genetic predisposition
  • Nutrient deficiency, including vitamins and minerals like B-12, zinc, folate, and iron
  • Hormonal changes, stress, and anxiety It is essential to note that the exact cause of aphthous ulcers is often unknown, and a comprehensive assessment is needed to diagnose and manage these ulcers effectively 1. In terms of morphological features, aphthous ulcers can manifest as well-demarcated, oval or round ulcers with a white or yellow pseudomembrane and a halo surrounding erythematous, but some cases may have atypical clinical symptoms, making diagnosis challenging 1. The diagnosis and treatment of aphthous ulcers require a thorough medical history inquiry, histopathological examination, and screening for systemic diseases, as outlined in the expert consensus guideline for diagnosis 1.

From the Research

Causes of Aphthous Ulcers

  • The exact cause of aphthous ulcers (canker sores) is not well understood, but several factors may play a role, including nutritional deficiencies 2.
  • Increased viscosity of oral submucosal extracellular matrix (ECM) is thought to contribute to the development of recurrent aphthous stomatitis (RAS) or canker sores 3.
  • Trauma to the oral mucosa can trigger the formation of aphthous ulcers, and irritants such as hard, acidic, and salty foods, as well as toothpastes containing sodium lauryl sulfate, can exacerbate the condition 4.
  • Hormonal influences, particularly sex hormones, may also play a role in the development of aphthous ulcers, especially in the early phase of exposure 3.
  • Immunodeficiency states, such as those associated with systemic diseases like Adamantiades-Behçet disease, can also increase the risk of developing aphthous ulcers 5, 6.
  • Dietary factors, including low intake of vitamin B12 and folate, have been linked to an increased risk of recurrent aphthous stomatitis 2.

Possible Triggers

  • Certain foods, such as gluten in patients with gluten-sensitive enteropathy, may trigger aphthous ulcers in individual cases 3.
  • Alcohol and carbonated drinks may also contribute to the development of aphthous ulcers 4.
  • Stress and other environmental factors may also play a role in triggering aphthous ulcers, although the exact mechanisms are not well understood 6.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Reduced dietary intake of vitamin B12 and folate in patients with recurrent aphthous stomatitis.

Journal of oral pathology & medicine : official publication of the International Association of Oral Pathologists and the American Academy of Oral Pathology, 2010

Research

The treatment of chronic recurrent oral aphthous ulcers.

Deutsches Arzteblatt international, 2014

Research

Diagnosis of oral ulcers.

The Mount Sinai journal of medicine, New York, 1998

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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