Causes:
The exact cause of aphthous ulcers is not known. However, it may occur due to the following causes:

• Stress
• Hormonal changes
• Injury while brushing, sports injury, accidental cheek bite, or while undergoing dental treatment 
• Eating extremely spicy food
• Sensitivity to certain food items 
• Viral infections 
• Nutritional deficiency
• Using mouth rinses and toothpaste that may contain sodium lauryl sulfate
• Presence of certain medical disorders, like:
• Celiac disease (sensitivity to gluten leading to an intestinal disorder)
• Behcet’s syndrome (a disease caused due to the inflammation of the body's blood vessels)
• Inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis 
• Conditions like HIV and AIDS, which suppress the body’s immune system

Risk factors:
Certain factors may increase the possibility of developing aphthous ulcers and may include the following:

• Family history of aphthous ulcers
• Commonly seen in females
• Teenagers and young adults
• Hormonal changes 
• Food allergies
• Abnormal immune system 

Symptoms:
The various aphthous ulcer symptoms are:

• Pain or soreness that usually subsides in a week or two
• Red bump that later develops into an open ulcer
• A single bump or group of bumps inside the mouth
• Ulcer with a yellow or white center
• Lesser common symptoms of aphthous ulcers include:
• Fever 
• Extensive scarring
• Cluster of ulcers
• Sore having irregular edges
• Sore more than 12 mm in diameter 
• Swollen lymph nodes

Diagnosis:

1. Visual examination: Aphthous ulcers can be visually identified by the dentist or doctor.
2. Medical history: The doctor inquires about the patient’s symptoms, medical history, family history, and any medications that the patient may be taking. 
3. Blood tests: These tests help to confirm the presence of any suspected medical disease that could lead to aphthous ulcers.
4. Biopsy: Suspected cancer growths that appear like an aphthous ulcer may need a biopsy to confirm or rule out cancer.

Treatment:

• The aphthous ulcer usually heals on its own without any treatment in approximately a week or two. Treatment may be provided for large, painful, and persistent aphthous in the following different ways:
• Mouth rinses:
• The doctor may prescribe a mouth rinse containing the steroid dexamethasone to reduce pain and inflammation.
• A mouth rinse containing lidocaine may be prescribed to reduce pain.

Topical products:
Certain pastes, liquids, gels, or creams may aid in reducing pain and promote rapid healing.
Examples of topical products may include hydrogen peroxide, benzocaine, and fluocinonide.

Oral medications:
Oral medications may be recommended when aphthous ulcers are severe, or the ulcers fail to respond to other topical treatments.
These medicines have serious side effects and are only used as a last resort.

Cautery:
A chemical substance or instrument is used for searing, burning, or destroying the ulcer.
Debacterol is a kind of topical solution applied to chemically cauterize the aphthous ulcers.
Silver nitrate also aids in chemically cauterizing aphthous ulcers and relieving pain.

Other treatments:
Nutritional supplements may be prescribed by the doctor.
Any underlying medical disease that may be causing the aphthous ulcer is treated.
Antibiotics like doxycycline may be prescribed by the doctor.

If an aphthous ulcer lasts for more than a couple of weeks, it can cause complications like:

• Fever
• Fatigue
• Pain or discomfort while eating, talking, or brushing teeth
• Sores spread outside the mouth
• Pain or discomfort while eating, talking, or brushing teeth
• Candida (fungal) infection
• Cellulitis (a common bacterial skin infection)