There are many reasons why there is a lump on the inside of the jawbone, such as sebaceous cysts, folliculitis, bone augmentation, tumors and so on. 1. Sebaceous cysts: excessive secretion of oil by sebaceous glands can lead to the blockage of sebaceous glands and the gradual formation of cysts, which can cause the phenomenon of a lump on the inside of the lower part of the jawbone. 2. Folliculitis: blockage of hair follicles in the skin of the jawbone or bacterial infection can induce folliculitis, thus showing the phenomenon of a pimple underneath the jawbone, which may be related to the lack of attention to local hygiene. 3. Bone protrusion: there is a lump under the mandible which may also belong to bone protrusion, usually occurring in the lingual side of mandibular bicuspid teeth, and the overall surface is very smooth. 3. Tumor: Mandibular tumors can also lead to the phenomenon of a lump under the mandible, which may belong to benign tumors or malignant tumors. There are many reasons why there is a lump underneath the mandible, and after the symptoms appear, it is recommended to go to the hospital in time to improve the examination, and take standardized treatment under the guidance of the doctor, so as not to ignore the symptoms and take them lightly, so as not to lead to adverse consequences.