The cause of tension-type headaches is not known. In the past, experts thought tension-type headaches were caused by muscle contractions in the face, neck and scalp. They thought the muscle contractions were a result of emotions, tension or stress. But research suggests that muscle contraction isn't the cause. The most common theory is that people who have tension-type headaches have increased sensitivity to pain. Muscle tenderness, a common symptom of tension-type headaches, may result from this sensitized pain system.