A headache is a common and usually mild to moderate pain in the head. It is often caused by stress, fatigue, or poor posture. A migraine is a more intense headache that is often accompanied by nausea, vomiting, and sensitivity to light and sound. Migraines can last for hours or even days and be very debilitating. The cause of migraines is not entirely known, but may be related to changes in brain chemistry or hormones. Treatment for both headaches and migraines can include over-the-counter medications or prescription medications.