Canker sore vs cold sore

Canker sores and cold sores aren’t the same. Here’s how to distinguish them.


It’s easy to mistake canker for cold sores. They’re both located in or around the mouth and they can look like small white blisters. But they have very different causes. Understanding what distinguishes canker sores from cold sores means you can get the right treatment for a speedy healing process.


What are cold sores?

Cold sores (also known as fever blisters) are small, white blisters that usually show up on your lip or around your mouth. In the early stages when a cold sore develops you may notice some redness and a tingling sensation. Eventually, the sores blister and a crust will form on top.

It takes an average of 10 to 14 days for cold sores to heal completely. 

Contrary to what their name suggests, they are not related to the common cold. But having a cold could weaken the immune system and provoke an outbreak of fever blisters.

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What causes cold sores?

Cold sores are caused by the herpes simplex virus type 1 (HSV-1) and more rarely HSV-2. HSV is incredibly infectious and spreads easily through contact with the skin, saliva and other bodily fluids.

Approximately 3.7 billion worldwide are carriers of HSV-1. Some of them may never develop a single cold sore whilst others suffer frequent outbreaks. There are certain triggers that can bring about cold sores:

  • UV rays (sunlight, tanning beds)
  • Very cold, windy or dry, hot weather
  • Stress
  • A weak immune system
  • Changes in hormone levels


Cold sores symptoms

The symptoms of a cold sore can include:

  • Swollen, red lips
  • Fluid-filled blisters on or surrounding the lips
  • Tingling, itchy or burning sensation
  • Yellow crust on the blister
  • Fever
  • Body aches


How to treat a cold sore?

Cold sores usually go away all by themselves. It takes up to 2 weeks for them to heal completely. But there are medications and home remedies to speed up the healing process.

Make sure you start treatment at the first sign of a cold sore emerging (usually within 48 hours). The longer you delay medical therapy, the more time it will take for symptoms to subside.

You can get over-the-counter antiviral creams such as Zovirax (acyclovir) and Denavir (penciclovir). These can be applied 2 to 5 times a day and usually offer quick relief.

If you’re prone to cold sores and get them multiple times a year, your doctor may prescribe oral antiviral medications such as valacyclovir or famciclovir. A single dose repeated once after 12 hours is usually enough to speed up the healing process.

When you’ve got cold sores, your immune system is working hard to fight the infection. You can help speed up the healing process by:

  • Eating a healthy, balanced diet
  • Taking vitamin supplements such as Vitamin C and E
  • Maintaining a regular exercise regime


Home remedies that may be beneficial against cold sores include:

  • Aloe vera gel (applied to the skin)
  • Lysine supplements (to boost the immune system)
  • Lemon balm (applied to the skin or taken as a supplement)
  • Zinc (taken as an oral supplement or applied to the skin in the form of zinc cream)


Cold sore prevention

There is no cure or vaccine for HSV-1 and even the best medication and home remedies won’t work wonders. Although they can reduce the average duration by 2 days, the best way to avoid cold blisters is to prevent them.

So, what can you do to prevent cold sores?

  • Do not touch the sores or your lips during an active breakout
  • Do not rub other areas of your body (e.g. your eyes or genitals) after touching your cold sore because you could spread the infection to these sensitive areas
  • Do not kiss someone if you have an outbreak and wait 3 to 4 days after the kiss blisters have healed completely
  • Do not share a toothbrush, towels, cutlery or other items that could come in contact with your mouth
  • Replace your lipstick or lip balm
  • Practice stress reduction techniques
  • Boost your immune system
  • Stay out of the cold or extreme heat


What is a canker sore?

Canker sores, also referred to as ulcers or aphthae, are painful, shallow lesions on the inside of the mouth. They are red or white in color. Canker sores are not contagious and usually go away after a week or two.

The main difference to cold sores is that they are not caused by HSV and they are not located on the outside of the mouth. However, you can get canker sores on the skin on the inside of the lower or upper lip.


What causes canker sores?

Canker sores can have lots of different causes including:

  • Trauma (biting or aggressive tooth brushing)
  • Infections caused by a lack of oral hygiene (e.g. when not washing your hands before touching the inside of your mouth)
  • Diet lacking in zinc, folate, vitamin B12 or iron
  • Allergies
  • Stress
  • Food sensitivity

Medical conditions such as celiac disease, HIV, Behcet disease and IBS could make you more prone to canker sores.

As with cold sores, a healthy immune system is vital to remedy ulcers quickly.


How to treat a canker sore?

When you have canker sores, the most important thing you can do is practice good oral hygiene.

  • Brush your teeth regularly but be careful not to brush too hard or to touch the sore
  • Rinse your mouth with antiseptic mouthwash or saltwater
  • Get an over-the-counter gel, like Anbesol or Orajel and apply it with a cotton bud (do not touch the area with your fingers)
  • You can also apply tea tree oil or sage to the affected area
  • Avoid eating or drinking foods that are spicy, salty, citrusy or easily get stuck in your teeth
  • Take painkillers such as ibuprofen if the sore is very painful

One research study found that patients applying mouth gel containing hyaluronic acid (e.g. Gengigel) saw a decrease in ulcer size after just 3 days compared to those rinsing with hyaluronic acid mouthwash.


How long do canker sores last?

Canker sores usually go away by themselves after 1 or 2 weeks. If they last longer, you should consult a dentist or doctor. They may prescribe a steroid paste or prescription mouthwash to treat the ulcer.

Though it’s rare, some patients have experienced canker sores at the back of their throats or on their tonsils. These may look bigger than usual canker sores and can cause scarring. They are more difficult to treat because they are harder to reach. Speak to a doctor if you’re having difficulty treating your canker sore.


How can I prevent canker sores?

Sometimes canker sores aren’t easily preventable. For example, you may accidentally bite your lip whilst chewing or you may experience an injury that causes damage to the soft tissues on the inside of your mouth.

But if you get ulcers more than once or twice a year, you should:

  • Boost your immune system by eating a healthy diet and adding physical activity to your daily routine
  • Avoid foods that could be triggering ulcer breakouts such as overly spicy ingredients
  • Take a good multivitamin supplement
  • Practice good oral hygiene
  • Reduce stress



You can easily tell the difference between a cold sore or a canker sore depending on their location (outside or inside of the mouth) and whether they are raised or flat.

Cold sores will usually look like bumps and after a week a crust should form on top of them. 

Canker sores are flat ulcers that will turn red as they begin to heal.

But whether you have cold sores or ulcers, they are both important signs that your immune system response is poor and shouldn’t be ignored. 



  1. [Internet]. Cologne, Germany: Institute for Quality and Efficiency in Health Care (IQWiG); 2006-. Cold sores: Overview. 2018 Jul 12. Available from:
  2. Harvard Health Publishing. (2015, April 28). Cold sores - Harvard Health. Retrieved November 6, 2019, from Harvard Health website:
  3. Chi, C. C., Wang, S. H., Delamere, F. M., Wojnarowska, F., Peters, M. C., & Kanjirath, P. P. (2015). Interventions for prevention of herpes simplex labialis (cold sores on the lips). The Cochrane database of systematic reviews, 2015(8), CD010095.
  4. Edgar, N. R., Saleh, D., & Miller, R. A. (2017). Recurrent Aphthous Stomatitis: A Review. The Journal of clinical and aesthetic dermatology, 10(3), 26–36.
  5. Canker Sores | Michigan Medicine. (2010). Retrieved November 7, 2019, from website:
  6. Dalessandri, D., Zotti, F., Laffranchi, L., Migliorati, M., Isola, G., Bonetti, S., & Visconti, L. (2019). Treatment of recurrent aphthous stomatitis (RAS; aphthae; canker sores) with a barrier forming mouth rinse or topical gel formulation containing hyaluronic acid: a retrospective clinical study. BMC Oral Health, 19(1).

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