Mouth ulcers, also known as canker sores, are unpleasant little sores that appear in your mouth; they look like round white, yellow, or grey sores.
They’re usually harmless and aren’t contagious, but they can be irritating and painful while you wait for them to heal.
Mouth ulcers can be caused by many things, like biting the inside of your cheek, poorly fitting dentures or braces, feeling tired, stressed or anxious; hormonal changes, and stopping smoking.