Mouth ulcers, spots or sores that don’t heal: when it’s normal and when to get checked

This is not a diagnosis (that is made in the clinic), but as a general guide:

Aphthous ulcer (canker sore):

  • usually a small, round/oval, painful ulcer with a white-yellowish center and a reddish border
  • commonly appears on mobile mucosa: inside the cheeks, lips, under the tongue
  • does not typically appear as grouped “blisters”

Irritation/trauma:

  • appears after biting, after very hard/sharp foods, after a filling with a rough edge, or a denture/appliance that rubs
  • may look like a red area, an abrasion, or an ulcer exactly at the contact point
  • improves if the cause is removed (adjustment, protection)

Herpes (usually HSV-1):

  • often starts with a burning/tingling sensation, followed by blisters that break and turn into lesions
  • commonly appears on or around the lips; intraorally it more typically appears on fixed mucosa (palate/gums), though variations exist
  • may recur during periods of stress, fatigue, or lowered immunity

If you have repeated episodes or it’s unclear what it is, an evaluation is recommended, especially if the lesion persists.

Common causes: why mouth ulcers and lesions appear

The most common causes or contributing factors include:

  • Local trauma: biting, aggressive brushing, hard foods, rough edges of a filling, cracked tooth
  • Stress and fatigue: in some people, ulcers occur more often during demanding periods
  • Nutritional deficiencies: sometimes associated with iron, B12, folate deficiency or other issues (especially when frequent)
  • Orthodontic appliances, dentures, dental work: can rub the mucosa and cause sores or ulcers
  • Chemical irritation: some mouthwashes or toothpastes may irritate (especially if overused)
  • Reflux, dry mouth, mouth breathing: can worsen irritation
  • General conditions: less commonly, recurrent lesions may be associated with certain systemic diseases or medication reactions (requires medical evaluation)

If you wear dentures or braces and frequently develop sores, proper adjustment can significantly reduce episodes.

Safe comfort measures at home

The goal is to reduce pain and support healing without further irritating the mucosa:

  • Avoid irritating foods: spicy, very acidic (citrus), very salty, very hot
  • Choose soft foods for a few days if chewing is painful
  • Maintain hygiene, but gently: brush normally without “scratching” the lesion
  • Gentle rinses with warm salt water (not aggressive, 1–2 times/day) if they help
  • Topical gels for ulcers (barrier/protective) or products recommended by a doctor/pharmacist for comfort
  • If you have braces/dentures causing injury, use orthodontic wax (for braces) or schedule an adjustment

What to avoid:

  • alcohol directly on the sore or very “strong” solutions that burn the mucosa
  • aggressive rinsing many times a day
  • self-medicating with antibiotics for such lesions (they usually don’t help)

If you have severe pain, a doctor may recommend local or systemic treatment depending on the cause.

When evaluation is needed: warning signs

Schedule a check-up if any of the following occur:

  • The lesion lasts more than 2 weeks (even if it doesn’t hurt)
  • It bleeds easily or spontaneously
  • It increases in size or changes appearance
  • Severe pain that prevents eating/sleeping
  • Swollen lymph nodes (neck/jaw area)
  • Fever, general malaise, or widespread lesions in the mouth
  • Very frequent recurrences (e.g., monthly or almost continuous episodes)
  • Persistent white/red patches, thickened areas, or ulcers with hard margins

These situations do not automatically mean something serious, but they should be checked.

Why screening matters and what the doctor may investigate

A check-up is not just “a quick look.” Depending on the appearance and context, the doctor may:

  • Identify a local cause: rough edge, filling, cracked tooth, improper bite, denture/appliance causing friction
  • Assess signs of infection or inflammation
  • Recommend local treatment (gels, rinses, protection), sometimes specific medication if it’s herpes or another cause
  • Recommend tests if ulcers are frequent (e.g., for iron/B12/folate deficiencies), in collaboration with your general practitioner
  • Monitor non-healing lesions and, if needed, suggest further investigations or referral to a specialist (e.g., ENT/oral and maxillofacial surgery evaluation)

Screening is important because some oral lesions can mimic ulcers or irritation, and the basic rule is simple: if it doesn’t heal within 2 weeks, it should be checked.

Useful questions for your consultation

  • Does it look like an ulcer/irritation or another type of lesion?
  • Is there a local cause (tooth, filling, appliance) maintaining it?
  • What local treatment is appropriate and how long should healing take?
  • If it recurs often, should I do tests for deficiencies?
  • What signs should make me return sooner?

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If you have a mouth sore that doesn’t heal, recurs frequently, or shows warning signs (lasting over 2 weeks, bleeding, growing, severe pain, swollen lymph nodes), the safest step is to get it checked.

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