Migraine (UK: /ˈmiːɡreɪn/, US: /ˈmaɪ-/) is a primary headache disorder characterized by recurrent headaches that are moderate to severe. Typically, episodes affect one side of the head, are pulsating in nature, and last from a few hours to three days. Associated symptoms may include nausea, vomiting, and sensitivity to light, sound, or smell. The pain is generally made worse by physical activity, although regular exercise may have prophylactic effects. Up to one-third of people affected have aura: typically a short period of visual disturbance that signals that the headache will soon occur. Occasionally, aura can occur with little or no headache following, but not everyone has this symptom.