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What Is a Canker Sore — and How Is It Different from a Cold Sore?

A canker sore (aphthous ulcer) is a shallow oval white-yellow ulcer with a red border that forms inside the mouth — on the inner cheek, under the tongue, lip, or gums. It is not contagious.

Common misconception: The Thai name "ron nai" comes from a traditional belief that ulcers are caused by "internal body heat." Modern research shows they result from an abnormal immune response combined with triggers like stress, nutritional deficiency, and minor trauma — not heat.

What Causes Canker Sores — 6 Triggers

Canker sores result from multiple triggers in people with genetic susceptibility to oral mucosal inflammation (about 40% have family history):

1. Mechanical trauma — biting the cheek or tongue, vigorous brushing, braces, dentures
2. Stress and poor sleep — reduce salivary IgA and suppress local immunity
3. Nutritional deficiency — especially B12, folate, iron, zinc (found in ~20% of chronic sufferers)
4. Hormonal change — premenstrual, pregnancy, menopause
5. SLS (Sodium Lauryl Sulfate) toothpaste — strips protective layer in sensitive individuals
6. Trigger foods — citrus, spicy foods, chocolate, nuts, coffee

Common locations: under the tongue (~30%), inner cheek (~25%), tongue tip/base (~20%), inner lip (~15%), gums (~10%). Tongue ulcers tend to hurt more due to dense nerve endings.

How Long Do Canker Sores Take to Heal?

Healing time depends on size and type — minor ulcers heal on their own in 7-14 days without medication.

Typical timeline:

• Day 1-2 mild tingling before the ulcer appears (prodromal stage)
• Day 2-4 white-red-rim ulcer visible; pain peaks
• Day 5-10 pain decreases, ulcer becomes shallower
• Day 10-14 ulcer fully closes, mucosa returns to normal

How to Soothe Canker Sores Faster

Most canker sores heal on their own. Home care focuses on reducing pain + preventing further irritation + reducing oral bacteria — not "curing" directly.

Home care (start with the simplest)

1. Warm saline rinse 2-3 times daily — 1/2 tsp salt in 1 cup warm water, swish 30 seconds
2. Avoid trigger foods — acidic, spicy, hot, sharp foods
3. Use a straw to minimize liquid contact with the ulcer
4. Switch to SLS-free toothpaste temporarily
5. Baking soda rinse (1/2 tsp in warm water) — helps adjust oral pH
6. Rest + reduce stress — stress is a major trigger

Supportive option — Propolis spray

Propolis is a natural resin produced by bees. Studies in NCBI and Cochrane Database suggest propolis extracts have anti-inflammatory effects that may help oral mucosa heal faster in some cases.

Propoliz Mouth Spray by Intimo Life is a Brazilian Green Propolis spray with finger root and honey — free of sugar and preservatives. It can be a supportive option while the ulcer heals, sprayed every 2-3 hours.

⚠️ Note: Propolis spray is not a "canker sore treatment" — it is a natural option that may improve comfort. If the ulcer is large, severely painful, or fails to improve within 7-10 days, consult a pharmacist about topical medication.

Medications a pharmacist or doctor may prescribe

• Triamcinolone acetonide 0.1% oral paste — topical corticosteroid, reduces inflammation
• Choline salicylate 8.7% gel — fast pain relief ⚠️ contraindicated under 16 years
• Lidocaine 2% oral gel — topical anesthetic for temporary pain relief
• Chlorhexidine 0.12% mouthwash — reduces oral bacteria, short-term use

You can consult an Intimo Life pharmacist via chat on our website — real pharmacist responses.

What to Eat and What to Avoid

Soft, cool foods rich in B12, folate, and iron help ulcers heal faster and reduce recurrence long-term.

Eat 🟢

• Cold yogurt (probiotic supports oral microbiome balance)
• Leafy greens (spinach, kale, broccoli — folate)
• Eggs, fish, poultry, liver (B12)
• Soy, tofu (iron)
• Warm rice porridge, congee, soup
• Ripe bananas, peeled apples, pears (non-citrus fruits)
• Plenty of water

Avoid 🔴

• Lemon, pineapple, orange, tomato (acidic)
• Chili, spicy foods
• Crackers, chips, dry cookies (sharp foods)
• Coffee, chocolate (triggers in some)
• Peanuts, walnuts (triggers in some)
• Very hot foods

How to Reduce Recurrence of Canker Sores

People with recurrent aphthous stomatitis (RAS) can reduce frequency with 6 basics — the most important is checking B12, folate, and iron levels.

1. Check B12 / folate / iron blood levels — a 2009 NCBI study (Volkov et al.) showed 6-month low-dose B12 supplementation significantly reduced RAS frequency
2. Sleep 7-9 hours/night — poor sleep suppresses local immunity
3. Reduce stress — light exercise, meditation, avoid sitting work over 90 minutes
4. Brush gently with soft bristles + daily floss
5. Switch to SLS-free toothpaste (Sensodyne Pronamel, Biotene, generic SLS-free brands)
6. Track personal trigger foods — observe meals 2-3 cycles to spot patterns

When to See a Doctor — 6 Warning Signs

Most canker sores are harmless and self-resolving. But these 6 signs warrant a doctor or dentist visit:

1. Ulcer larger than 1 cm or unusually deep
2. No improvement within 14 days
3. Recurring several times per month (RAS — Recurrent Aphthous Stomatitis)
4. Accompanied by fever, swollen lymph nodes, fatigue
5. Oral ulcers combined with ulcers on genitals, eyes, or skin (possible Behçet's disease)
6. Difficulty swallowing, breathing, or speaking clearly

You can also consult an Intimo Life pharmacist on our website — real pharmacist responses.