A sore inside your mouth may not actually be a cold sore. Cold sores, caused by the herpes simplex virus (HSV-1), almost always appear on the outside of the mouth, around the lips. Sores that show up on the inner cheeks, tongue, or soft tissue inside the mouth are usually canker sores, which have a completely different cause and need different care. Getting this distinction right matters because the treatments are not interchangeable.
Cold Sore or Canker Sore: How to Tell
Cold sores appear as clusters of small, fluid-filled blisters, typically on or around the lips. They’re caused by HSV-1, they’re contagious, and they often start with a tingling or burning sensation hours before blisters form. Canker sores, by contrast, show up inside the mouth on the cheeks, tongue, or inner lips. They look like a single round white or yellow sore with a red border, and they are not contagious.
Canker sores have no known viral cause. They can be triggered by mouth injuries (biting your cheek, irritation from braces), stress, smoking, or deficiencies in folic acid, iron, or vitamin B12. If you’re dealing with a single pale sore inside your mouth that isn’t blistered, you almost certainly have a canker sore rather than a cold sore.
That said, HSV-1 can occasionally cause sores on the gums or hard palate, especially during a first outbreak. These intraoral herpes sores still look like clusters of small blisters rather than the smooth, crater-like shape of a canker sore. If you’re unsure which type you have, the blister-versus-crater distinction is the most reliable visual clue.
How to Treat a Canker Sore
Most canker sores heal on their own within one to two weeks without any treatment. To speed things along and reduce pain, rinse your mouth several times a day with warm salt water (about half a teaspoon of salt in a cup of water). Over-the-counter oral gels that contain a numbing agent can provide temporary relief, especially before eating. Avoid spicy, acidic, or rough-textured foods that irritate the sore.
If your canker sores are unusually large, last longer than two weeks, or keep coming back, a doctor or dentist can prescribe a stronger topical treatment or investigate whether a nutritional deficiency is driving them.
How to Treat a Cold Sore
If your sore really is a cold sore (blistered, on or near the lips, preceded by tingling), the goal is to shorten the outbreak and manage pain. Cold sores typically resolve within 5 to 15 days, but treatment started early can shave time off that window.
The over-the-counter cream docosanol (sold as Abreva) is the main non-prescription antiviral option. In a large clinical trial of over 700 patients, people who used docosanol healed in a median of 4.1 days, about 18 hours faster than those using a placebo. The key is applying it at the very first sign of tingling, before blisters form. Once blisters have fully appeared, topical treatment is far less effective.
For people who get frequent or severe outbreaks, prescription antiviral medications work significantly better. These are taken as pills rather than applied topically. Your doctor may prescribe a short course at the start of an outbreak, or if you get six or more outbreaks per year, daily suppressive therapy to prevent them from occurring in the first place.
The Five Stages of Cold Sore Healing
Understanding the stages helps you know what to expect and when you’re most contagious.
- Prodrome (hours to one day): Tingling, burning, or itching at the site before anything is visible. This is the best window to apply antiviral treatment.
- Swelling and discoloration: The skin reddens and a small bump forms.
- Blistering: Small fluid-filled blisters cluster together, usually on one side of the lips. You are highly contagious at this point.
- Crusting (around 48 hours after blistering): Blisters break open, ooze, and form a scab. Resist the urge to pick at it.
- Healing: The scab falls off and the skin heals completely. Total time from first tingle to resolution is typically 5 to 15 days.
How to Avoid Spreading the Virus
Cold sores spread through direct skin contact and saliva. While you have an active sore, avoid kissing, sharing utensils, cups, straws, or lip balm. Don’t touch the sore with your fingers. If you do touch it, wash your hands immediately. Touching an active cold sore and then touching another part of your body can transfer the virus to a new site. HSV-1 infections on the fingers, called herpetic whitlow, happen exactly this way.
Children with cold sores who suck their thumbs are especially prone to spreading the virus to their fingers. Keep the area clean and discourage touching.
Common Triggers for Outbreaks
HSV-1 stays dormant in nerve cells after the initial infection and reactivates periodically. Knowing your triggers can help you reduce how often outbreaks happen. The most well-documented triggers include:
- Stress and anxiety: Psychological distress has a significant association with recurrent outbreaks.
- Sun exposure: Ultraviolet light, particularly UV-B, is one of the most common reactivation triggers. Wearing lip balm with SPF helps.
- Fatigue and poor sleep: Physical exhaustion lowers immune defenses enough to allow reactivation.
- Illness or fever: The common cold and other infections are classic triggers, which is where the name “cold sore” comes from.
- Poor diet: Diets low in fruits and vegetables, combined with inadequate hydration, have been linked to more frequent episodes.
You can’t eliminate every trigger, but managing stress, wearing SPF lip protection outdoors, getting enough sleep, and eating a balanced diet collectively reduce the frequency of outbreaks for most people. If cold sores keep recurring despite these measures, daily suppressive antiviral therapy is an option worth discussing with your doctor.