The two bags in the back of the neck are commonly caused by the following reasons: 1, local hair follicle infection, when the hair follicle infection can form sebaceous cysts, which is caused by the accumulation of many powder-like infected material in the hair follicle, you need to go to the hospital to improve the relevant examination. If this is the case, it needs to be surgically removed, otherwise it will lead to localized redness, pain, and even ulceration and pus. 2. Lipoma formation, a benign mass, is caused by the abnormal accumulation of fat particles in the body. If the disease is considered after ultrasound, there is usually no need to worry too much and regular follow-up can be done. However, if the swelling increases further or becomes painful, it needs to be removed surgically and sent for pathological examination.3. It may be caused by mosquito bites, which can be treated by applying local ointment, baking soda, iodophor, etc.4. There are other causes, such as enlarged lymph nodes. In short, if it continues to increase, you need to go to the hospital to check the cause in time.