What causes aphthous ulcers (canker sores)?

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Last updated: April 22, 2025View editorial policy

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From the Guidelines

Canker sores are 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, as stated in the expert consensus guideline for diagnosis 1. The exact cause of canker sores, also known as recurrent aphthous ulcers (RAU), is unknown in some cases, but it may be caused by disturbed immune response, genetic predisposition, nutrient deficiency, oral trauma, anxiety or stress 1. Some key factors that contribute to the development of canker sores include:

  • Minor injuries to the mouth, such as accidental cheek bites or rough brushing
  • Food sensitivities, particularly acidic or spicy foods
  • Nutritional deficiencies, especially vitamin B-12, zinc, folate, or iron
  • Hormonal changes
  • Stress
  • Possibly genetic factors
  • Overreaction of the immune system, where the body attacks the normal cells in the mouth lining It is essential to note that the diagnosis and treatment of oral ulcers, including canker sores, are tasks of oral specialists, and a comprehensive assessment is needed to determine the underlying cause and develop an effective treatment plan 1. In terms of treatment, options typically involve over-the-counter topical products containing benzocaine or hydrogen peroxide for pain relief, while prescription options include steroid mouth rinses, antibiotics, or cauterizing medications for larger or more painful sores. To prevent recurrence, it is recommended to maintain good oral hygiene, use a soft-bristled toothbrush, avoid irritating foods, and consider taking a multivitamin if deficiencies are suspected. If you experience unusually large, painful, or frequent canker sores that last longer than three weeks, you should consult a healthcare provider as this could indicate an underlying condition.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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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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