Canker Sore

By Tiffany Tseng. May 7th 2016

Ever wondered what that painful, raised, white circle with an inflamed border on your gum or the inside of your mouth is? It is none other than the infamous canker sore, also known as an aphthous ulcer or recurrent aphthous ulcer (RAS). Canker sores usually appear on the membrane inside of the oral cavity, most commonly on the inside of the lips, inside of the cheeks, the soft palate or on the gums. However, canker sores can also appear on or under the tongue. While it can almost be unnoticeable, any oral activity, such as chewing, talking or drinking, may cause it to be tender and painful. They can appear as individual sores, or clusters of blisters in more serious cases.

Contrary to popular belief, canker sores are not contagious and cannot be transmitted by saliva or sharing drinks or food. They are commonly mistaken with cold sores or fever blisters, which are caused by herpes simplex or other oral bacteria. While similar in appearance, cold sores occur outside of the oral cavity rather than inside.


While the exact cause of canker sores is unclear, there seems to be several factors that may trigger the appearance of the sores, including:

  • Emotional, physical or social stress
  • Lack of sleep
  • Weakened immune system
  • Hormonal changes
  • Menstrual periods
  • Allergies to toothpastes or mouthwashes
  • Deficiency in folate, B vitamins, and zinc
  • Imbalance of nutrients in the diet

Also, minor physical trauma to the mouth can also create these painful lacerations. Common ones include:

  • Improper tooth brushing techniques
  • Hard toothbrush bristles
  • Sharp and abrasive foods (such as chips, pretzels, cereal, granola, etc)
  • Harsh and acidic foods (such as coffee, spicy foods, citruses, salty foods, etc)
  • Dental devices (such as dentures and braces)
  • Accidental biting of the tongue or cheek

Signs and Symptoms

Before any evident physical signs, the site of the canker sore will feel tender and sensitive. Then, within a few days, the sore will change from an irritated red bump to a painful open sore. The appearances of the lesion are usually round, about the size of the tip of a pencil eraser, with an inflamed red border and a white pus-like middle forming a small crater with an elevated border. Any oral activity will irritate the sore, and they can appear in small clusters or just one single sore.

If other symptoms, such as fever, fatigue or swollen lymph nodes, are also present along with canker sores, it is advisable to get a check up with your physician or dentist. If the sore lasts more than several weeks, it should also be looked upon to rule out other conditions, as as canker sores are sometimes indications of other, more serious health illnesses.


There are generally three classifications of canker sores.

  • Simple Canker Sore: Simple canker sores can last up to a week, and may occur several times a year. This is probably the most common type of canker sore.
  • Complex Canker Sore: Complex canker sores tend to be larger than simple canker sores, and have the same general appearance as simple canker sores. They are extremely painful, and may take more than a month to heal and can possibly leave a scar.


Mild forms of canker sores will heal by themselves from anywhere between a few days to a week. While medical treatment isn't usually necessary, there are several home remedies that can help relieve the pain during the waiting time.

There are also several, over-the-counter oral medications that can be obtained at the local pharmacy. They are usually variations of antibiotics, anesthetics or anti-inflammation medications that are safe to be applied within the oral cavity. They can come in the form of topical creams and gels, sprays or tablets to be swallowed. Be sure to follow all instructions on the package for your safety.

In more serious cases of canker sore, your physician or dentist may prescribe stronger versions of medication, including variations of analgesics, anesthetics agents, corticosteroids, antiseptics, anti-inflammatory agents, steroids, sucralfate, tetracycline suspension and silver nitrate. However, these are usually reserved for individuals who have chronic flare-ups or have serious cases of canker sores.

Sometimes, braces are the culprit of canker sores, or can irritate your sores, causing extreme pain. In that case, be sure to notify your dentist or orthodontist as soon as possible to alleviate the situation. Your dentist or orthodontist can provide you with a special wax that can be applied over your braces to allow the canker sore to heal without irritation.


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