Mouth ulcers are small, painful sores that can appear on the soft lining of the mouth, including the gums, lips, tongue, inner cheeks, or roof of the mouth. They are usually harmless and heal on their own within one to two weeks.

Some people have a condition called aphthous ulcers, which are recurring ulcers with no known cause. Around 20% of the population is affected by aphthous ulcers.Mouth ulcers can be alarming. However, they're not a sexually transmitted infection (STI) and you can't get or spread them from kissing or sharing food and drinks. Aside from any pain and discomfort, mouth ulcers are usually harmless and go away on their own in a week or two.