The lump on the left side of the neck may be enlarged lymph nodes in the neck, thyroid nodules and sebaceous cysts, etc. It is recommended to go to the hospital to clarify the cause of the disease and then treat the cause. 1. Lymph nodes in the neck, when infected by bacteria, fungi and viruses, will have inflammatory reactions, and the inflammatory factors will stimulate the lymph nodes and cause the lymph nodes to become enlarged and painful. 2. Thyroid nodules, the formation of which occurs under the stimulation of many factors, such as iodine deficiency, radiation, and hormone synthesis disorders. It can cause the thyroid tissue to proliferate and become enlarged. 3. If you don’t have a regular routine, don’t pay attention to cleanliness and hygiene, and stay up late for a long time, which leads to endocrine disorders, it will cause a large amount of oil secretion, and sebaceous cysts will be formed after the opening of sebaceous glands is blocked, which will be manifested as a lump in the neck. The above are only some of the common causes. Therefore, it is recommended to go to the hospital as soon as possible to find out the cause of the lump on the left side of the neck, and actively cooperate with the doctor to receive standardized treatment to promote the healing of the disease.