Canker sores develop inside your mouth, like on your gums or cheeks. With some exceptions, cold sores usually form on the outside of the mouth on the lips.

The oral lesions caused by canker sores and cold sores may appear and feel similar, but they actually have different causes.

Canker sores occur only in the soft tissues of the mouth, such as on your gums or inside your cheeks. They can be caused by a variety of factors, including injury to the inside of your mouth and vitamin deficiencies.

Cold sores form on and around your lips, although in some cases they can also form inside your mouth. They’re caused by infection with the herpes simplex virus (HSV).

Read on to learn more about the differences between canker sores and cold sores.

Canker sores

Canker sores occur only on the inside of your mouth. They can be found in the following areas:

  • gums
  • inside your cheeks or lips
  • on or below your tongue
  • soft palate, which is the soft, muscular area found in the back area of the roof of your mouth

You may notice a burning or tingling feeling before canker sores appear.

Canker sores are typically round or oval in shape. They can appear to be white or yellow, and may have a red border.

Canker sores can also vary in size from small to large. Large canker sores, which can also be referred to as major canker sores, may be quite painful and take longer to heal.

Herpetiform canker sores, a less common type of canker sore, occur in clusters and are the size of pinpricks. This type of canker sore typically develops later in life.

Cold sores

The symptoms of a cold sore can depend on if you have a new infection with HSV or have had the virus for a while.

Those with a new infection may experience:

  • burning or tingling, followed by the development of painful sores on or around the lips, in the mouth, on the nose or other areas of the face
  • sore throat or pain when you swallow
  • fever
  • body aches and pains
  • headache
  • nausea
  • swollen lymph nodes

If you’ve had the virus for a long time, you may experience periodic outbreaks of cold sores. These outbreaks typically follow several phases, including:

  1. warning signs in the area of the outbreak, which can include a burning, stinging, or itching sensation
  2. appearance of cold sores, which are filled with fluid and are often painful
  3. crusting over of the cold sores, which happens when the cold sores break open and form scabs
  4. healing of cold sores, typically without a scar, in one to two weeks.

How do I tell the difference?

The location of the sore can often help you tell if it’s a canker sore or a cold sore. Canker sores only occur inside the mouth while cold sores often occur on the outside of the mouth around the area of the lips.

Most people are infected with HSV during childhood. After a new HSV infection, children under age 5 may have cold sores inside of their mouth that can sometimes be mistaken for canker sores.

Canker sores

Researchers are still unsure what exactly causes canker sores, but unlike cold sores, canker sores aren’t contagious. You can’t get them from activities such as sharing eating utensils or kissing.

Some of the possible triggers can be one or a combination of the following:

  • injury to the inside of your mouth
  • deficiency in nutrients such as vitamin B-12, iron, or folate
  • use of toothpastes or mouthwashes that contain sodium lauryl sulfate
  • stress
  • fluctuations in hormones, such as those that occur during menstruation
  • a reaction to foods such as chocolate, nuts, or spicy foods
  • conditions that affect your immune system, such as lupus and inflammatory bowel diseases

Cold sores

Cold sores are caused by infection with specific strains of HSV. HSV-1 is the strain that most commonly causes cold sores. However, HSV-2, the strain that causes genital herpes, can also cause cold sores.

HSV is very contagious. The virus is most contagious when oozing cold sores are present, although it can be transmitted even if cold sores aren’t present.

HSV-1 can be spread through things such as sharing eating utensils or toothbrushes, or through kissing. Oral sex may spread HSV-2 to the mouth and lips, and may also spread HSV-1 to the genitals.

After you’ve contracted the infection, some factors may lead to the development of cold sores, including:

  • stress
  • fatigue
  • being sick with the flu or a cold
  • sunlight exposure
  • changes in hormones, such as during menstruation
  • irritation to the area where you have cold sores, which can be due to injury, dental work, or cosmetic surgery

You should seek medical attention for any mouth sore that:

  • is unusually large
  • doesn’t heal after two weeks
  • recurs frequently, up to several times in a year
  • causes extreme difficulty with eating or drinking
  • occurs along with a high fever

Your doctor will often be able to tell if you have a canker sore or a cold sore based on your medical history and a physical examination.

In order to confirm a diagnosis of cold sores, they may take a sample from the sore to be tested for HSV.

If you have canker sores that recur often, your doctor may also perform blood tests to check for nutritional deficiencies, food allergies, or immune conditions.

Canker sore

Small canker sores typically don’t require treatment and will disappear on their own within a week or two.

For larger or more painful canker sores, there are several treatment options, including:

  • over-the-counter (OTC) creams and gels that can be applied directly to sores, especially those that contain active ingredients such as benzocaine, hydrogen peroxide, and fluocinonide
  • prescription mouthwashes containing dexamethasone, a steroid that can ease pain and swelling
  • oral medications, such as steroid medications, which can help when canker sores don’t respond to other treatments
  • cautery, which involves using a chemical or instrument to destroy or burn the canker sore

If underlying health problems or nutrient deficiencies are causing your canker sores, your doctor will work with you to treat those as well.

Cold sores

Like canker sores, cold sores typically go away on their own within a few weeks. There are some treatments that can help ease symptoms and speed up healing, including:

  • OTC creams or gels containing lidocaine or benzocaine to ease pain
  • OTC cold sore creams containing docosanol, which may shorten your outbreak by about a day
  • prescription antiviral drugs, such as acyclovir,valacyclovir, and famciclovir

Both canker sores and cold sores should clear up on their own within a week or two. Some medications may help to speed up the recovery process.

If you have a mouth sore that doesn’t go away after two weeks, you should see your doctor.

While the exact cause of canker sores is uncertain, you can help prevent them by doing things such as protecting your mouth from injury, eating a healthy diet, and reducing stress.

Most canker sores will go away on their own in a week or two.

Cold sores are caused by HSV infection. Once you have the infection, you have the virus for your lifetime. Some people with HSV will never have cold sores while others will experience periodic outbreaks.

Cold sores should clear up on their own in a few weeks, although antiviral medications may speed healing. You should be particularly conscious to avoid skin-to-skin contact or the sharing of personal items when you have a cold sore, as this could spread the virus to others.