From the photograph, this looks like a small area of irritation or minor injury on the inner lip. It could be related to accidental biting, rubbing against a tooth, or minor trauma. A photograph alone cannot confirm the exact cause.
Next Steps
Avoid biting or rubbing the area and observe it for the next 1–2 weeks. It should gradually become smaller and heal. If it does not improve, becomes larger, painful, bleeds, or keeps coming back, please get it examined by a dentist/oral medicine specialist.
Health Tips
Maintain good oral hygiene and avoid spicy or very hot foods if they irritate the area. Do not pick or repeatedly touch the spot. If you notice that a sharp tooth, filling or denture is rubbing against it, have it checked by your dentist.
Any mouth lesion that does not heal within about 2 weeks should be professionally examined, particularly if it persists or changes in appearance.