Doctors are still unsure why canker sores develop, but they tend to form inside the mouth. Cold sores result from a viral infection, and they are more common on or around the mouth.
Canker sores are painful round or oval lesions that form on soft tissue inside the mouth, such as on the tongue or inner sides of the lips or cheeks.
Cold sores are caused by the herpes simplex virus. They can appear on or around the lips, but they may develop elsewhere on the face or on the tongue, gums, or throat.
Below, we compare the symptoms and treatments of canker sores and cold sores.
When trying to identify a canker sore or a cold sore to find the right treatment, it can help to know about the following differences:
Canker sores form in the softer areas inside the mouth, such as the tongue, cheeks, lips, and soft palate — which is at the back of the roof of the mouth.
These sores are not contagious. They are very common, affecting more than half of the United States population.
They heal without treatment but may reappear at the same location or in a different spot.
There are three forms of canker sores, which are known medically as aphthous stomatitis:
- Minor aphthous stomatitis: These sores are under 1 centimeter in diameter and heal within about 1 week, without causing scars.
- Major aphthous stomatitis: These sores are larger than 1 centimeter in diameter, can last for more than a couple of weeks, and can cause scarring.
- Herpetiform aphthous stomatitis: The least common type, these are clusters of tiny sores that sometimes merge to form larger ones. They usually take a little over 1 week to heal.
During childhood, most people develop an infection with the herpes simplex virus responsible for cold sores.
Some people never develop symptoms. If symptoms occur right after the initial infection, during childhood, they may include:
- a burning sensation, then the formation of painful sores — cold sores — on the lips, gums, tongue, or throat
- a sore throat
- pain while swallowing
- swollen lymph nodes
- a fever
- aches and pains
- a headache
These may last 1–2 weeks.
Cold sores can reappear, and the outbreaks typically become less severe over time. Symptoms of a cold sore follow a three-step pattern:
- First, a person may feel a burning, itching, or stinging sensation in a spot on or around the mouth.
- Second, a fluid-filled blister, the sore, develops at the spot.
- Third, the blister breaks, oozes, and crusts over, all within about 48 hours of the initial warning sensations.
In people who are healthy, cold sores usually disappear within 5–15 days, without causing scarring. If a cold sore lasts longer than 15 days, a person should receive medical attention.
Also, anyone with a cold sore near their eyes should see a doctor immediately.
Cold sores are contagious. Wash the hands well and regularly to prevent them from spreading.
Understanding the underlying causes can also help a person differentiate between the two types of lesions.
While the exact cause of canker sores is still a mystery, The American Academy of Oral Medicine (AAOM) explain that they may result from immune system dysfunction in the soft tissue lining of the mouth.
These sores can also form, the AAOM note, as an allergic reaction to food, toothpaste, or mouthwash.
In addition, canker sores can be a sign of another condition, such as a gastrointestinal disease. For this reason, a doctor may recommend taking a culture or a biopsy of a sore.
Anyone who has canker sores and any of the following symptoms should speak with a doctor:
- abdominal pain
- a fever
- eye discomfort
- rashes or sores elsewhere
Also, it is a good idea to notify a dentist if more than three canker sore outbreaks occur each month or any canker sores do not resolve within 10–14 days.
A form of the herpes simplex virus causes cold sores, and once the virus enters the body, it never leaves.
People with cold sores can spread the infection through:
- sharing utensils
- sharing personal items such as towels
Cold sore outbreaks can be triggered by:
- illness, such as cold
- injury to areas where sores once appeared
- dental work
- cosmetic surgery
- sunburn or just exposure to strong sunlight
- certain foods
- hormonal changes, such as during a period
Cold and canker sores respond to different treatments.
While there is no cure for canker sores, some over-the-counter or prescription medications can cause the sores to heal more quickly and appear less often.
Treatments for canker sores fall into a few categories:
- Occlusive agents: These are protective coatings that shield nerve endings and protect against irritation from temperature changes and certain foods. One example is benzyl alcohol gel.
- Cleaning agents: These clear bacteria and debris from the surface of the lesion. One example is a solution of 3% hydrogen peroxide mixed with an equal amount of water.
- Anesthetics: These reduce the pain. The most common anesthetic for this purpose is benzocaine, though some people are allergic to it.
Sometimes an ingredient in toothpaste called sodium lauryl sulfate can trigger canker sore outbreaks. Some people may benefit from avoiding toothpastes that contain it.
If sores are moderate to severe, avoid self-treatment and consult a doctor.
Learn more about treating canker sores here.
Depending on the severity of a cold sore outbreak, a doctor may prescribe topical, oral, or injectable antiviral medications.
Some prescription antiviral treatments include:
- docosanol or acyclovir cream
- acyclovir, valacyclovir, or famciclovir pills
- intravenous foscarnet or cidofovir
Some people require pain relief medication, such as topical lidocaine.
To prevent cold sores on the lips from worsening, a person should apply lip balm with a sun protection factor, or SPF, of 30 or higher.
If a person does not receive treatment for cold sores, they can spread, and some people become very ill as a result of the infection.
It is not always possible to prevent canker sores or cold sores from forming. However, the following strategies may help.
The AAOM recommend keeping track of when canker sores appear in a journal.
This can help a person detect any triggers, which may involve foods, types of toothpaste or mouthwash, and lifestyle factors.
To possibly prevent the sores from appearing, doctors recommend using antiviral treatment at the first warning sign, which may be a burning or stinging sensation.
People who get cold sores often may benefit from a prescription cream called penciclovir (Denavir). It helps reduce the amount of time that the sores appear on the skin.
Several other health issues can cause lesions that may look like cold or canker sores, including:
- certain blisters
- autoimmune conditions
- oral cancer
Anyone who is unsure about the type or cause of a lesion in, on, or around the mouth should speak with a doctor.
Cold sores and canker sores are both common, and they may look alike.
However, their causes, symptoms, and treatments are different.
Canker sores typically occur on soft areas inside the mouth. Though cold sores may also appear on the tongue, throat, or gums, they tend to form on or around the mouth.
Also, the herpes simplex virus causes cold sores, but doctors are still unsure of the exact cause of canker sores.
Finally, cold sores require treatment to prevent the infection from spreading, while canker sores typically disappear on their own.