The causes of a stiff neck and shoulder may include poor posture, stress, a muscle sprain in that area or a headache. Stiffness may also be caused by poor ergonomic conditions and is often accompanied by shoulder and arm pain. In more severe cases, a stiff neck and shoulder may be due to an underlying medical condition such as meningitis. Poor sleeping positions, particularly when the head and neck are improperly supported, may also cause shoulder and neck problems.

A stiff, sore neck and shoulder pain is commonly associated with bad sitting or standing posture. When the weight of the head is not properly balanced, stress is placed on the head and shoulders, which results in stiffness and pain. Stiffness in the neck and shoulders caused by poor posture is often correctable without medical intervention. Some, however, may need to wear a back brace or specialized clothing to correct poor posture and relieve shoulder and neck pain.

Stress is also a common cause of a stiff neck and shoulder. Many people have a tendency to unconsciously tighten the shoulder muscles when preoccupied with worry and anxiety. This results in soreness and a stiff neck and shoulder. Prolonged stiffness may also cause chronic pain in these areas.

Often, stiffness in the shoulder and neck indicates a serious medical condition. One such condition, meningitis, is treatable by prescription antibiotics. In addition to shoulder and neck stiffness, an infected person may also experience nausea, headache and vomiting. While anyone can contract the bacteria that causes this disease, it most commonly occurs in young children.

Muscle sprains commonly cause a stiff neck and shoulder. Such can happen due to an athletic injury, placing too much stress on the neck and shoulders, or from improper posture while exercising. When a stiff neck and shoulder are caused by a muscle sprain, resting those muscles is necessary to relieve pain and discomfort. Anti-inflammatory medications and a light massage may also help.

Headaches caused by tension, food allergies, a lack of quality rest and repetitive or prolonged work may also contribute to a stiff neck and shoulder. A caffeine dependency or skipping meals may also cause a headache, which may trigger the symptoms of a stiff neck and shoulder. Often, symptoms are relieved by rest and over-the-counter or herbal headache remedies. Those with chronic headache symptoms, however, may need medical attention.