A canker sore, or aphthous ulcer, is a lesion that develops on the soft tissues that line the inside of the mouth, gums, and inner lips.

A canker sore on the inside of the lip can appear as a white or yellow open wound surrounded by inflamed tissue. Canker sores are not contagious. People may notice a tingling or painful sensation in tissue on and near a canker sore. Eating, drinking, and speaking can exacerbate these symptoms.

In this article, we discuss causes, risk factors, and treatments for a canker sore on the lip.

Canker sores have no known causes. Researchers have identified numerous factors associated with canker sores, including:

  • genetics
  • infections
  • physical or emotional stress
  • food intolerance or allergies
  • injury or damage to the tissues of the mouth
  • hormonal changes, such as those experienced during menstrual cycles, pregnancy, and menopause
  • nutritional deficiencies, such as low iron, vitamin B12, and folic acid
  • blood disorders, such as Sutton Disease II or Behcet’s disease

A research article in BMC Oral Health indicates the following factors may increase the chances of developing a canker sore on the lip:

  • injury or tissue damage due to dental work, sports accident, or accidentally biting the lip
  • using oral hygiene products that contain sodium lauryl sulfate
  • poor oral hygiene that leads to bacterial overgrowth in the mouth
  • eating spicy or acidic foods
  • eating foods that trigger allergic reactions, such as eggs, nuts, dairy, or chocolate
  • changes in hormone levels
  • experience intense or chronic emotional stress
  • having a weakened or overactive immune system

In one 2014 study, researchers investigated canker sore occurrence in 3,244 people from India. They found that canker sores primarily affected females and adults in their 30s and 40s.

A canker sore is a round, white, or yellow sore that forms on the soft tissue inside the mouth. A person can develop a single canker sore or clusters of canker sores at a time.

Canker sores are usually recurrent, non-contagious, and heal within 4–14 days without treatment.

According to one article, there are three types of canker sore. These include minor, major, and herpetiform.

A minor canker sore is smaller than 5 millimeters (mm) in diameter and moderately painful.

Major canker sores are larger than 5 mm. People usually only develop one or two major canker sores at one time. These canker sores can lead to significant pain and discomfort, especially while eating, drinking, or speaking.

A major canker sore can take several weeks or months to heal.

Herpetiform canker sores occur when a cluster of pinpoint ulcers fuse, forming one large, irregularly shaped lesion. This is the rarest form, accounting for 5–10% of all canker sore diagnoses.

A doctor can diagnose a canker sore based on a physical exam. They may also ask about a person’s current symptoms and whether they have a history of mouth sores, nutritional deficiencies, or other canker-sore risk factors.

A doctor may order laboratory tests, such as blood work or a swab culture of the lesion. They use these tests to rule out other potential diagnoses, such as cold sores and bacterial infections.

Most canker sores heal on their own without medical treatment. However, certain over-the-counter (OTC) and prescription treatments can help prevent infection and promote healing.

Treatment options for a canker sore on the lip include:

OTC gel, paste, or patch

An over-the-counter (OTC) gel or paste, such as Orajel, soothes canker sore pain and shields it from external irritants, such as food and bacteria.

Inner mouth patches cover open sores inside the mouth. These patches protect against irritants and promote faster healing.

OTC anti-inflammatory drugs

Acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs) can help relieve pain and reduce inflammation.

Medicated mouthwash

Mouthwash containing hydrogen peroxide, chlorhexidine, or zinc sulfate prevents the growth of harmful microorganisms, such as bacteria. Antiseptic mouthwashes may also promote faster healing and prevent canker sores in the future.

Some prescription mouthwashes contain a local anesthetic or a corticosteroid to relieve pain and reduce inflammation.

Systemic treatments

A doctor may recommend one of the following medications if a person experiences severe canker sores that do not respond to more conservative treatments:

  • sucralfate (Carafate), which people typically use to treat intestinal ulcers
  • colchicine (Mitigare) is a potent anti-inflammatory that people use to treat gout
  • prescription oral corticosteroid, such as prednisone

Home remedies

People may manage and help treat canker sores at home with these steps:

  • drinking warm chamomile tea with honey
  • chewing or suck on ice chips to numb a canker sore
  • maintaining good oral hygiene
  • using a soft toothbrush
  • limiting or avoiding spicy or acidic foods
  • limiting or avoiding food sensitivities, such as eggs, nuts, coffee, or chocolate
  • eating foods rich in folic acid and iron, such as legumes and leafy greens
  • taking a vitamin B12, iron, or folic acid supplement

Click here to learn more about ways to treat canker sores.

Both canker sores and cold sores are small, common, painful lesions that can cause a burning or tingling sensation. While they may look alike, their causes, symptoms, and treatments are different.

The herpes simplex virus causes cold sores, but doctors are still unsure of the exact cause of canker sores.

Typically, canker sores appear inside the mouth, while cold sores tend to appear on or around the mouth.

Cold sores are also contagious and require treatment to prevent the infection from spreading. Canker sores are not contagious and typically disappear on their own.

Click here to learn more about canker sores vs. cold sores.

Most canker sores heal on their own within a few days to a week. A person should contact their doctor if their canker sore does not heal after 2–3 weeks despite using OTC or other home treatments.

People should also seek medical treatment if they have a canker sore that significantly impairs their ability to eat, drink, or speak.

A canker sore on the lip can cause significant pain and discomfort. However, most canker sores heal quickly without requiring medical treatment.

OTC mouth gels, antiseptic mouthwashes, and NSAIDs can help relieve pain, reduce inflammation, and prevent infections. Treating a canker sore can speed up the healing process.

People should speak with a doctor if they have a severe canker sore that does not respond to OTC or at-home treatment.

Canker sores can occur as a result of nutritional deficiencies. People who are low in iron or folic acid may want to consider eating more beans, lentils, and leafy greens.

Consult a healthcare provider before starting a new supplement.