Accidental lip biting (most common cause)
Repeated chewing or sucking of the lip
, injuries
Sharp teeth or orthodontic appliances causing chronic irritation
When a salivary gland duct is damaged, saliva leaks into the connective tissue, forming a soft, fluid-filled swelling called an extravasation mucocele. So check for any such lip bite.
Next Steps
This needs a small intervention, the surgeon will do excision, giving you local anesthesia there, suture 2-3 absorbable ones ,hardly 10 minutes procedure.
Health Tips
check for irritant causes, and avoid them to prevent recurrences.