What causes canker sores

Overview

Canker sores, medically known as aphthous ulcers or aphthous stomatitis, are small, painful mouth sores that typically develop on the inner cheeks, lips, gums, or tongue. While usually benign and self-healing, canker sores can be uncomfortable and interfere with eating and speaking. Understanding causes helps prevent recurrence and determine when professional evaluation is needed.

Minor Mouth Injuries

Accidental mouth trauma is the leading cause of canker sores. Causes include aggressive toothbrushing that damages soft tissues, dental braces and sharp wires, accidentally biting the cheek or lip, sharp foods like chips or hard candies, or minor dental procedures. The injury triggers inflammation and ulcer formation. Most trauma-related canker sores develop within 24 hours of injury and heal naturally in 1-2 weeks without treatment.

Nutritional Deficiencies

Deficiencies in essential nutrients increase canker sore frequency and severity. Vitamin B12 deficiency is particularly common in vegetarians and those with absorption issues. Iron, folate, and zinc deficiencies impair mouth tissue health and immune function, increasing susceptibility. Blood tests can identify deficiencies. Supplementation or dietary changes including B12 foods (meat, fish, dairy), iron-rich foods (spinach, beans), and zinc sources (oysters, pumpkin seeds) reduce canker sore occurrence.

Dietary Triggers

Acidic foods irritate mouth tissues and frequently trigger canker sores in susceptible individuals. Common culprits include citrus fruits (oranges, lemons, limes), pineapple, strawberries, and tomatoes. Spicy foods cause similar irritation. Sodium lauryl sulfate, a foaming agent in many toothpastes, may irritate sensitive mouths. Switching to SLS-free toothpaste and avoiding trigger foods during active sores helps reduce pain and prevent recurrence.

Stress, Sleep, and Immune Factors

Chronic stress and sleep deprivation suppress immune function and reduce mouth tissue integrity, making canker sores more likely. High-stress periods often correlate with canker sore outbreaks. Certain autoimmune conditions including Behçet's disease cause recurrent severe canker sores. Hormonal changes during menstruation also trigger sores in some women. Managing stress through relaxation techniques and ensuring adequate sleep helps prevent stress-related canker sores.

When to Seek Medical Attention

Most canker sores heal within 1-2 weeks without treatment. However, consult a healthcare provider if sores are unusually large (over 1 cm), persist longer than 3 weeks, are extremely painful despite treatment, frequently recur, interfere significantly with eating, or are accompanied by fever or swollen lymph nodes. These signs may indicate nutritional deficiencies, autoimmune conditions, or infections requiring professional evaluation.