Pain on the left side of the neck is rarely seen in cancer, most of them are caused by neck muscle spasm, such as prolonged head bowing, sleeping pillows are too high or too soft, which may lead to neck muscle spasm, patients with this symptom should consult a doctor in time to find out the cause of the disease. The chances that the pain on the left side of the neck is cancer are very small. Cancer in its early stage usually does not cause localized pain or discomfort in other parts of the body. However, if the patient has pain symptoms for a long time, it may also be lymphoma or thyroid cancer. When feeling neck pain, the first thing that should be suspected is that it is caused by improper posture during sleep. Prolonged lying on the left side of the body or inappropriate pillow height, softness or hardness can lead to local muscle spasm, congestion, edema, the formation of aseptic inflammation, and the appearance of pain. In addition, if there is a localized infectious disease on the left side of the neck, it can also cause pain, because the infection will cause local redness, swelling, heat and pain. If the pain on the left side of the neck is caused by bad postural habits, pay attention to lying down and rest, and you can give appropriate hot compresses and physical therapy to relieve the symptoms. If the pain is caused by other unknown reasons, go to orthopedics or general surgery to find out the cause. Patients should eat a light diet and less spicy food to avoid aggravating the symptoms.