The causes of bulging at the back of the neck include canker sores, fat pads and lipomas. 1. Carbuncle: After the skin at the back of the neck is infected by Staphylococcus aureus, it can lead to multiple follicles being involved, resulting in a bulge, which is accompanied by redness and pain in the skin of the infected area, and in severe cases, abscesses can be formed, and even generalized fever. 2. Fat pad: fat pad, also known as rich package, mostly refers to the fat accumulation in the back of the neck to form a lump-like bump, mostly caused by long time working with head down, looking at the cell phone and other bad posture, preferably in the obese people, in addition to the back of the neck of the mild patients bulging bags without obvious clinical symptoms, the serious cases can have limited neck activities, upper limb weakness, numbness, tingling and so on. 3. Lipoma: Lipoma can appear when fat tissue accumulates abnormally at the back of the neck, which is a benign tumor, generally without other uncomfortable symptoms, mostly related to excessive fat intake, irregular life and work and metabolic abnormalities. The bulge at the back of the neck can also be caused by other reasons, it is recommended to improve the auxiliary examination, after a clear diagnosis for targeted treatment.