Mouth on Fire? Why Your Canker Sore Stings & Medically Approved Relief

If you've ever had a canker sore, you know the feeling. That small white or yellow ulcer inside your mouth can make eating, drinking, and even talking uncomfortable. Spicy food feels like fire. Citrus stings. Even brushing your teeth can hurt.

The good news? Most canker sores are harmless and heal on their own. But understanding why they hurt—and what actually helps—can make a big difference in how quickly you recover and how much discomfort you feel.

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What Is a Canker Sore?

A canker sore (also called an aphthous ulcer) is a small, shallow lesion that develops on the soft tissues inside your mouth. Unlike cold sores, they are:

• Not contagious
• Not caused by herpes
• Found inside the mouth (cheeks, lips, tongue, or soft palate)

They usually appear as:

• A round or oval sore
• White, yellow, or gray center
• Red border around the edge

Most canker sores heal within 7–14 days without scarring.

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Why Does a Canker Sore Sting So Much?

The pain isn't your imagination. A canker sore stings for real biological reasons.

1. Nerve Exposure

A canker sore is essentially an open ulcer. The protective top layer of skin (mucosa) is damaged, exposing sensitive nerve endings underneath. When food, drinks, or air touch it, those nerves send pain signals.

2. Inflammation

Your immune system reacts to the ulcer by sending inflammatory cells to the area. This causes:

• Redness
• Swelling
• Increased sensitivity

Inflammation helps healing, but it also makes the area more painful.

3. Acid and Irritation

Acidic foods (like tomatoes and citrus), salty snacks, and spicy meals can irritate the exposed tissue. Even toothpaste containing sodium lauryl sulfate (SLS) may worsen discomfort for some people.

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What Causes a Canker Sore?

In many cases, the exact cause of a canker sore isn't clear. However, several triggers are known to increase risk.

Common Triggers

• Minor mouth injury (biting your cheek, dental work, aggressive brushing)
• Stress or lack of sleep
• Hormonal changes
• Acidic or spicy foods
• Food sensitivities (such as chocolate or nuts)

Nutritional Deficiencies

Low levels of certain nutrients may play a role:

• Iron
• Vitamin B12
• Folate
• Zinc

If you get frequent canker sores, it may be worth discussing nutrient testing with your doctor.

Medical Conditions

Recurring or severe canker sores may be linked to:

• Celiac disease
• Inflammatory bowel disease
• Immune system disorders
• Behçet's disease

If sores are frequent, unusually large, or slow to heal, medical evaluation is important.

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Types of Canker Sores

Not all canker sores are the same.

1. Minor Canker Sores (Most Common)

• Small (less than 1 cm)
• Heal within 1–2 weeks
• Do not scar

2. Major Canker Sores

• Larger and deeper
• Can last several weeks
• May scar
• More painful

3. Herpetiform Canker Sores

• Clusters of tiny ulcers
• Can merge into larger sores
• Not related to herpes despite the name

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Medically Approved Relief for Canker Sore Pain

There is no instant cure, but there are effective, evidence-based ways to reduce discomfort and support healing.

✅ Topical Treatments (Applied Directly to the Sore)

These are often the most effective.

• Over-the-counter oral gels with benzocaine to numb pain
• Hydrocortisone dental paste to reduce inflammation
• Prescription corticosteroid gels or rinses for severe cases

Apply after meals and before bed for best results.

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✅ Antimicrobial Mouth Rinses

• Saltwater rinse (½ teaspoon salt in warm water)
• Baking soda rinse
• Prescription chlorhexidine mouthwash (for frequent or severe sores)

These help reduce bacteria and may prevent secondary infection.

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✅ Pain Relief Medication

If discomfort interferes with eating or speaking:

• Acetaminophen
• Ibuprofen (if safe for you)

Always follow dosing instructions and speak with a doctor if unsure.

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✅ Protective Pastes

Barrier pastes form a protective coating over the canker sore, shielding exposed nerves from irritation.

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✅ Nutritional Support

If deficiency is suspected:

• Vitamin B12 supplementation
• Iron supplements
• Folate or zinc as directed by a doctor

Do not self-supplement long term without medical guidance.

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What to Avoid While Healing

To prevent worsening pain:

• Spicy foods
• Citrus fruits
• Salty chips
• Crunchy or sharp foods
• Alcohol-based mouthwash
• Toothpaste with SLS (if sensitive)

Switching to a softer diet for a few days can reduce irritation significantly.

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When Should You Be Concerned?

Most canker sores are harmless. However, you should speak to a doctor if you notice:

• A sore lasting longer than 3 weeks
• Extremely large ulcers
• Severe pain that doesn't improve
• Frequent outbreaks (more than 3–4 times per year)
• Fever or feeling unwell
• Difficulty swallowing
• Sores spreading to lips or outside the mouth

While rare, persistent ulcers can sometimes signal more serious conditions, including immune disorders or oral cancer. Canker sores are a form of stomatitis, and if you're experiencing recurring mouth ulcers or unusual symptoms, a free AI-powered symptom checker can help you understand whether your symptoms warrant a doctor's visit.

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How Long Does a Canker Sore Last?

For most people:

• Minor sores: 7–14 days
• Major sores: Several weeks

Pain usually peaks during the first 3–4 days, then gradually improves.

If pain worsens instead of improving, medical advice is recommended.

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Can You Prevent Canker Sores?

You can't always prevent a canker sore, but you can reduce your risk.

Prevention Tips

• Use a soft-bristled toothbrush
• Avoid foods that trigger outbreaks
• Manage stress with sleep and relaxation techniques
• Maintain good oral hygiene
• Address vitamin deficiencies
• Consider SLS-free toothpaste

If canker sores are frequent, your doctor may recommend preventive medications or further testing.

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The Bottom Line

A canker sore can feel intense for something so small. The stinging sensation happens because sensitive nerve endings are exposed and inflamed. While uncomfortable, most canker sores are temporary and not dangerous.

Effective relief options include:

• Topical numbing gels
• Anti-inflammatory dental pastes
• Gentle mouth rinses
• Avoiding irritating foods
• Over-the-counter pain relievers

If sores are large, persistent, or frequent, it's important to speak to a doctor. In rare cases, recurring mouth ulcers can signal an underlying medical issue that needs attention.

Your mouth shouldn't feel like it's on fire for weeks. If something doesn't seem right—or if symptoms interfere with eating, drinking, or daily life—get professional medical advice promptly.

Most of the time, though, with the right care and a little patience, your canker sore will heal and your mouth will feel normal again soon.