Most canker sores are round or oval with a white or yellow center and a red border. They form inside your mouth — on or under your tongue, inside your cheeks or lips, at the base of your gums, or on your soft palate. You might notice a tingling or burning sensation a day or two before the sores actually appear. There are several types of canker sores, including minor, major and herpetiform sores. Minor canker sores Minor canker sores are the most common and:  Are usually small Are oval shaped with a red edge Heal without scarring in one to two weeks  Major canker sores  Major canker sores are less common and:  Are larger and deeper than minor canker sores Are usually round with defined borders, but may have irregular edges when very large Can be extremely painful May take up to six weeks to heal and can leave extensive scarring  Herpetiform canker sores Herpetiform canker sores are uncommon and usually develop later in life, but they're not caused by herpes virus infection. These canker sores:  Are pinpoint size Often occur in clusters of 10 to 100 sores, but may merge into one large ulcer Have irregular edges Heal without scarring in one to two weeks 
canker sores round oval white yellow center red border  form inside mouth — tongue  inside cheeks lips  base gums  soft palate  notice tingling burning sensation day sores actually appear  types canker sores  including minor  major herpetiform sores  minor canker sores minor canker sores common and:  small oval shaped red edge heal scarring weeks  major canker sores  major canker sores common and:  larger deeper minor canker sores round defined borders  may irregular edges large can extremely painful may take weeks heal can leave extensive scarring  herpetiform canker sores herpetiform canker sores uncommon develop later life  they're caused herpes virus infection  canker sores:  pinpoint size occur clusters 10 100 sores  may merge large ulcer irregular edges heal scarring weeks 
canker sore