Mouth Ulcers: Causes, Care and When to Get Checked

Not every mouth sore is an aphthous ulcer. Irritation, injury and other conditions can look similar. A sore lasting over three weeks, growing, bleeding or differing from your usual ulcers needs assessment. Seek help sooner for severe symptoms.

What Is a Canker Sore?

A canker sore (aphthous ulcer) is a painful white or yellow lesion on the oral mucosa, surrounded by a red ring. It is commonly seen:

• On the tongue
• On the inner surface of the cheek
• Inside the lip
• On the gums
• On the palate

Most canker sores heal on their own within 7-14 days and leave no scar.

What Are the Types of Canker Sores?

Minor Canker Sores

The most common type.

• Smaller than 1 cm
• Heal within 1-2 weeks
• Leave no scar

Major Canker Sores

Larger and deeper lesions.

• More painful
• Can take 2-6 weeks to heal
• May leave a scar

Herpetiform Canker Sores

Many small canker sores forming in clusters. The name comes from a herpes-like appearance, but it is not related to the cold-sore virus.

Why Do Canker Sores Appear?

The exact cause of canker sores is not fully known, but there are many trigger factors.

1. Trauma Inside the Mouth

Accidentally biting the cheek, using a hard toothbrush, or orthodontic wires can cause small injuries inside the mouth.

2. Stress and Lack of Sleep

Intense stress and irregular sleep can affect the immune system and increase the occurrence of canker sores.

3. Vitamin and Mineral Deficiency

The following deficiencies in particular are linked with recurring canker sores:

• Vitamin B12
• Iron
• Zinc
• Folic acid

4. Certain Foods

In some people, the following foods can trigger canker sores:

• Tomatoes
• Lemon
• Spicy foods
• Chocolate
• Nuts

5. Hormonal Changes

Hormonal fluctuations such as the menstrual cycle can make some people more prone to canker sores.

6. Toothpaste Ingredients

Toothpastes containing Sodium Lauryl Sulfate (SLS) can irritate the oral mucosa and increase how often canker sores occur.

7. Systemic Conditions

Frequently recurring canker sores can sometimes be linked to conditions such as:

• Celiac disease
• Crohn’s disease
• Ulcerative colitis
• Immune system disorders

How Do Canker Sores Heal?

Most canker sores heal on their own, but some methods can speed up healing and reduce pain.

Topical Creams and Gels

Used on a doctor’s recommendation:

• Corticosteroid gels for canker sores
• Local anesthetic gels
• Antiseptic mouth rinses

can help reduce discomfort.

Salt Water Rinse

Warm salt water or a baking-soda rinse can soothe the inside of the mouth.

Pay Attention to Oral Hygiene

• Use a soft-bristled toothbrush
• Brush without irritating the inside of the mouth
• Maintain regular oral care

Diet

During a canker sore flare-up, it helps to avoid:

• Acidic
• Spicy
• Hard
• Very hot foods

Drink Plenty of Water

Dry mouth can worsen canker sore discomfort. Drinking enough water during the day is important.

How Long Does It Take for a Canker Sore to Heal?

Most canker sores:

• Heal within 7 to 14 days
• Disappear without leaving a scar

However, large or recurring canker sores can take longer.

When Should You See a Dentist?

Professional evaluation is essential in the following cases:

• If the mouth sore lasts longer than 3 weeks
• If it keeps recurring
• If the number of sores keeps increasing
• If fever and fatigue accompany it
• If the sore keeps growing
• If it causes severe pain

Mouth sores that do not heal for a long time should always be evaluated.

Canker Sore or Cold Sore?

Canker sores and cold sores are often confused.

Canker Sore

• Forms inside the mouth
• Not contagious
• Not caused by a virus

Cold Sore

• Usually appears around the lips
• Caused by the HSV-1 virus
• Contagious

Frequently Asked Questions

Are canker sores contagious?

No. Canker sores are not contagious.

Why do canker sores keep recurring?

Vitamin deficiencies, stress, immune system problems, or certain systemic conditions can cause recurring canker sores.

Which vitamin deficiency matters most for canker sores?

The most commonly investigated deficiencies are:

• B12
• Iron
• Zinc
• Folic acid

Does stress cause canker sores?

Yes. Stress can affect the immune system and make canker sores more likely to form.

Related treatment and assessment

• Dental Check-Up and Examination

This information does not replace an individual assessment. At your appointment, explain when symptoms began and share details of medicines and previous treatment.

Source and further reading

• NHS: Mouth ulcers