Cold and Flu

Fever Blisters and Canker Sores

Fever blisters and canker sores are painful oral abrasions. A fever blister is an eruption of the skin appearing on the lips, gums, and other parts of the mouth. Sometimes these blisters can even appear inside the nose. Canker sores are ulcers and are commonly located on the inside of the mouth. These ulcer-like sores are yellow and white in color. A fever blister, unlike a canker sore, is very contagious. Canker sores cannot be spread from one person to another. In most cases, neither fever blisters nor canker sores require a doctors visit, though there are exceptions.

Common Underlying Causes of Fever Blisters and Canker Sores

Fever Blisters

The primary cause of a fever blister is the herpes simplex virus (HSV). There are two types of HSV; type 1 is typically the cause of oral herpes (fever blisters), while type 2 causes genital herpes. However, either type may affect the oral tissues. Each fever blister contains fluid with the virus inside. The herpes simplex virus can be spread from one person to another through kissing, drinking or eating after others, and touching other peoples hands that have come into contact with the blister. After your blister goes away, the virus continues to live inside the body forever. Some factors may increase the frequency of outbreaks. These “triggers” include:

  • overexposure of sun
  • lower immune functioning or illness, such as cold
  • periods of high stress

Canker Sores

The actual cause of a canker sore is unknown. Some common “triggers” and contributing factors of canker sores include:

  • hormone changes just before menstruation
  • an abrasion inside the mouth
  • consumption of hot beverages or foods
  • intestinal conditions, like Crohns disease or ulcerative colitis
  • vitamin B12 deficiencies
  • chemotherapy treatment

When To Seek Medical Attention

Fever blisters and canker sores are not typically emergency situations, as these sores go away after a few days to a couple of weeks. However, recurrent and frequent canker sores may be indicative of a serious underlying medical condition, such as oral cancer. If the sores do not go away after a few days or worsen, seeking prompt medical attention may improve your prognosis. Also, if you are unsure whether you have the herpes simplex virus, seeking immediate testing can help you determine whether or not you are contagious.

Addressing and Easing Symptoms

If preventative home health options, such as those below, do not lessen the symptoms of your fever blister or canker sore, see your doctor to rule out more serious conditions and to receive additional treatment options.

Home Health Options

There are a number of actions that you can take at home to lessen the symptoms of your fever blisters or canker sores.


Fever Blisters

  • An over-the-counter painkiller, such as aspirin or ibuprofen, may help relieve some pain.
  • Place ice on your blister to help numb the area and reduce any discomfort.
  • Over-the-counter medications that contain docosanol, such as Abreva, can be used to help treat and shorten the duration of your blisters. Applying this consistently may help dry out these blisters.

Canker Sores

  • Nonprescription topical medications with benzocaine and mouth rinses may help temporarily relieve pain.
  • Get adequate vitamin B12 by consuming dairy products, fish, and shellfish may help reduce your risk of developing more canker sores.
  • Avoid acidic, hot, and spicy foods, as these may worsen your symptoms.
  • Limit the consumption of foods that can stick to the sides of cheeks or gums, such as chewing gum, candy, and potato chips.

What Happens at the Doctors Office

Your doctor will likely take an inventory of your symptoms, as well as a complete medical history. Additionally, he or she will examine your mouth and any oral sores. To diagnose whether you have a fever blister or a canker sore, your physician may run some tests.

Fever Blisters

You doctor can test the fluid from your blister for the herpes simplex virus. If the virus is present, your doctor can prescribe medication that is more powerful than the over-the-counter treatments to reduce the duration of these symptoms and the frequency with which they occur. Research shows that certain prescription antiviral medications are the most effective form of treatment for both types of HSV. There are several medications available that may be administered orally (pills) or by injection:

  • Acyclovir
  • Famciclovir
  • Valacyclovir

When taken on a daily basis, these medications can lessen the frequency of outbreaks and make them less severe. They may also help prevent an infected person from spreading the virus to others.

Canker Sores

A medical doctor or dentist can examine the inside of your mouth to confirm a canker sore diagnosis. If a more serious medical condition is suspected, your doctor may order a complete blood count test to determine if nutritional deficiencies or an underlying medical condition are present. Your physician or dentist may prescribe an antibiotic to speed up your recovery. Also, he or she might recommend a prescription mouthwash with tetracycline to relieve pain and speed up the recovery.

Consequences of Untreated Fever Blisters or Canker Sores

Fever blisters and canker sores are not typically serious conditions. However, obtaining a diagnosis of the herpes simplex virus for your fever blister can inform you of the contagious nature of your sore. This information can prevent you from spreading the virus to others. Persistent canker sores may rarely indicate a serious underlying medical condition, such as oral cancer or other oral condition. Seeking prompt medical advice may improve your prognosis.

Preventing Fever Blisters and Canker Sores

There are several actions that you can take to prevent fever blisters and canker sores. Listed below are some preventative methods that may lessen the frequency of these oral sores.

Fever Blisters

  • Take measures to prevent contracting the herpes simplex virus, such as: not drinking or eating after others; washing your hands frequently; avoiding contact with sores or hands that may have touched the sores
  • Avoid overexposure of the sun.
  • Wear a sunscreen lip balm to protect your lips from the sun.

Canker Sores

  • Consuming foods rich in vitamin B12, such as milk and fish, may help reduce your risk of developing a canker sore.
  • Ingesting zinc and garlic may reduce the frequency of canker sores.
  • Practice good oral hygiene by brushing your teeth after eating, flossing, and rinsing with mouthwash.
  • Avoid foods that you know can cause an allergic reaction.
  • Avoid extremely acidic foods.
  • Stop smoking, as smoking is linked to an increased occurrence of mouth sores.