Medically known as ‘Aphthous Stomatitis’, these ulcers are often found inside the mouth on the mucous tissue like the inside of a cheek, on the tongue etc. These ulcers are red lesions with a yellow or white center. A slight swelling, pain, a burning sensation in the mouth and at times fever are some symptoms of canker sores. Though the exact cause of these sores is unknown, a few causes of canker sores are hormonal changes in the body, smoking too much, over stress, getting hurt in the mouth, and a weak defense system. Hereditary factors could also cause sores along with anemia, infections, a few medications, and food allergies. Usually, these sores disappear within a week or 10 days without any treatment.