These two mouth problems are often confused but have different causes and care.
Canker sores (Aphthous ulcers)
- What they are: Small, shallow ulcers inside the mouth (inner lips/cheeks, tongue, soft palate). Not contagious.
- What they look like: Round/oval sores with a white-yellow center and a red rim.
- Common triggers: Minor mouth trauma (braces, biting), stress, certain foods (acidic/spicy), sodium lauryl sulfate toothpaste, vitamin deficiencies (B12, iron, folate), hormonal shifts.
- Symptoms: Sore or burning spot, pain with eating/talking; no blisters on the outside of the lips.
Care and treatment
- Avoid triggers; switch to SLS-free toothpaste.
- Rinse with saltwater or baking soda solution.
- Over-the-counter options: protective pastes/patches, benzocaine gels, hydrogen peroxide rinses.
- Prescription options if frequent/severe: topical steroid gels/ rinses (e.g., triamcinolone in dental paste), doxycycline mouth rinse short course, or colchicine in recurrent severe cases (specialist care).
- Pain tips: cold drinks, ice, avoid acidic/spicy foods and alcohol-based mouthwashes.
When to see a clinician
- Ulcers larger than 1 cm, lasting >2 weeks, very frequent recurrences, weight loss, fever, or sores elsewhere (genitals/eyes).
- Very painful clusters that prevent eating/drinking.
- New ulcers after starting a medication (possible drug reaction).
Note: Recurrent severe ulcers can rarely be linked to conditions like celiac disease, inflammatory bowel disease, Behçet’s disease, or immune issues—evaluation helps if symptoms are atypical.
Cold sores (Fever blisters, Herpes labialis)
- What they are: Contagious blisters on or around the lips caused by herpes simplex virus (usually HSV-1).
- What they look like: Grouped tiny blisters on a red base that crust and heal in 7–10 days.
- Triggers: Illness/fever, sun exposure, stress, dental work, chapped lips.
Care and treatment
- Start treatment at the first tingle/burn if possible:
- Antiviral creams (docosanol OTC; acyclovir/penciclovir by prescription) can shorten duration if started early.
- Oral antivirals (valacyclovir, acyclovir, famciclovir) are most effective for frequent or severe outbreaks; ask your clinician about a “just-in-case” supply.
- Comfort: cool compresses, petroleum jelly to reduce cracking, pain relievers.
- Prevent triggers: use lip sunscreen; manage stress and avoid excessive sun/wind.
Contagion and precautions
- Avoid kissing and sharing drinks, utensils, or lip balms during an outbreak.
- Don’t touch the sores; wash hands if you do. Avoid contact lenses after touching a sore.
- Be cautious around babies, pregnant people, and anyone with weak immunity.
Key differences at a glance
- Location: Canker sores are inside the mouth; cold sores are typically on the lips/skin outside.
- Cause: Canker sores are not viral; cold sores are HSV and contagious.