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Canker Sores


Canker Sores are painful ulcers that usually occur inside the mouth, unlike cold sores that appear outside the oral cavity. The medical terminology for canker sores is aphthous ulcers. They occur on the mucosal lining of cheeks, lips, tongue, palate, and gums. Canker sores are small-sized ulcers with a whitish or yellow base surrounded by a red area. Another thing that differentiates canker sores from cold sores is that they aren’t contagious. Therefore the risk of getting canker sores by coming in contact with an affected person is non-existent.


The exact cause of canker sores has not been identified yet. From various research studies, it has been understood that canker sores can occur when the body’s T-cell mediated immune response is triggered. This can happen by multiple causes, including stress, anxiety, hormonal imbalance, nutritional deficiencies, food allergies, or dehydration. In certain cases, canker sores may appear as a result of direct or indirect traumatic injury to the soft tissue lining of our oral cavity. This includes injury by a dental procedure, inadequate or over-done fillings, ill-fitting prosthetic appliances, or constant trauma by braces. External factors such as smoking or alcohol might be contributing factors as well. Patients with certain genetic diseases or immunocompromising diseases such as cancers, HIV/AIDS, systemic lupus erythematosus, etc., can develop canker sores due to weakened immune systems.


Depending on the size and time required for healing, canker sores are divided into:

Minor canker sores: Minor canker sores are the most common type of this disease and frequently occur within a year whenever the immune response is triggered. They are small-sized ulcers. They have a yellow base and red border and can be painful to some extent. Minor canker sores heal within one or two weeks with or without medication.

Major canker sores: Major canker sores are excruciating ulcers limiting a person’s food and water intake. They’re comparatively less common than minor canker sores. They are usually large, round ulcers with a deep yellow base and well-defined red borders. Major canker sores take up to four to six weeks to heal completely with scarring.

Herpetiform canker sores: Herpetiform canker sores are an uncommon type that usually occurs in the very late stage of life. The herpes simplex virus does not cause these but is instead named such due to their similar appearance as cold sores. They usually appear in small clusters with or without a defined border. In some cases, these clusters may join to form a giant ulcer. In most cases, they take one or two weeks for complete healing.

Risk Factors and Epidemiology

The risk factors for canker sores include hormonal imbalance (especially during stress or menses), dietary insufficiency, frequent dehydration, smoking, alcohol, and certain food allergies. If you have dentures or any other dental appliance that might damage the soft tissues inside your mouth, you may risk developing canker sores. Additionally, patients with weakened immune systems, immunocompromising diseases, or certain genetic disorders risk developing these ulcers.  

Canker sores occur more commonly in females than males. They can occur at any age, but usually, they form after the age of 10. Therefore they’re uncommon in younger children.

Signs and Symptoms

If you’re to develop canker sores, you might experience a tingling or burning sensation along the mucosal lining inside your mouth before the ulcer develops. In many cases, the ulcers, whether minor or major, are painful and cause extreme discomfort. Small bumps or large crater-like ulcers may develop following the burning sensation. In severe cases, they can cause fever, swelling, malaise, irritability, and difficulty in eating.


Canker sores are generally diagnosed based on history and clinical examination. Your doctor will require a detailed medical history to identify any possible cause and rule out other diseases with similar symptoms. Upon clinical examination, the size, color, and location of these ulcers aid in diagnosis. In rare cases, a biopsy may be necessary to rule out the suspicion of oral cancer.

Differential Diagnosis

Other conditions that mimic the signs and symptoms of canker sores include cold sores, food and drug allergies, herpes simplex virus infection, lichen planus, oral candidiasis, erythema multiforme, and initial stages of squamous cell carcinoma (oral cancer).


Most canker sores are treated by home remedies and do not require professional medical help. Saltwater rinses or rinses with half part hydrogen peroxide and half part water are the most effective ways to reduce the pain and speed up the recovery process of canker sores. Topical analgesics or topical anesthetics containing lignocaine can be applied for temporary pain relief. Extremely hot or spicy foods should be avoided at all costs during the healing period. There is no permanent cure for canker sores. However, it is necessary to consult your doctor if these ulcers persist for more than fourteen days or present along with other complicated symptoms.


In certain cases of a large painful ulcer, topical corticosteroid ointments such as those containing dexamethasone are prescribed to control pain and reduce inflammation.


The overall prognosis for canker sores is good. In the majority of the cases, canker sores heal by themselves without any particular medication or treatment within two weeks. Larger ulcers may take longer to heal, but they resolve as well within six weeks. Only in cases where an ulcer persists for over two weeks and doesn’t show any sign of healing is it essential to look for other possible causes such as oral cancer.


The primary methods to reduce the occurrence of canker sores include proper maintenance of oral hygiene by brushing twice a day, flossing, and using ethanol-based or antiseptic mouthwashes. At least twice a year, regular visits to your dentist are always beneficial. If you have already developed canker sores once, it is important to understand your trigger factors and manage to reduce the chances of their recurrence.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr.Saad Zia on May 14, 2023.



Canker sore - Symptoms and causes - Mayo Clinic


Canker sore Information | Mount Sinai - New York


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