Mucous cyst: This is the most common cause of a cyst on the lip. It occurs due to the obstruction of a minor salivary gland duct, leading to the accumulation of mucin and formation of a cyst. The cyst is usually translucent, blue-colored, and filled with a clear gelatinous fluid.

Lipoma: A benign tumor composed of fat tissue that can occur on the lip, although it's less common than a mucous cyst.
Dermoid cyst: A congenital cyst that can occur on the lip, containing skin and sometimes other tissue like hair or teeth.
Epidermoid cyst: A benign cyst filled with keratin, a protein found in skin, hair, and nails, which can occur on the lip.
Fordyce spots: Small, yellowish or white bumps on the lips that are actually ectopic sebaceous glands, not true cysts but can be mistaken for them.

Squamous cell carcinoma: Although rare, a cystic appearance on the lip could be a sign of this type of skin cancer, especially in older adults or those with significant sun exposure.
Basal cell carcinoma: The most common form of skin cancer, which can rarely present as a cystic lesion on the lip.
Keratoacanthoma: A low-grade malignancy that can resemble a cyst and has a tendency to regress spontaneously but can be aggressive in some cases.

Branchial cleft cyst: A congenital anomaly that can present as a cyst on the lip or near the jawline, resulting from abnormal development of the branchial arches.
Thyroglossal duct cyst: Although typically found on the neck, in rare cases, it can occur on the lip if the thyroglossal duct opens abnormally during embryonic development.
Cystic hygroma: A congenital malformation of the lymphatic system that can rarely present as a cystic lesion on the lip.