Headaches can occur as a result of many conditions. There are a number of different classification systems for headaches. The most well-recognized is that of the International Headache Society, which classifies it into more than 150 types of primary and secondary headaches. Headache is a condition that’s one of the most common causes of pain and a major reason people miss work or school—and visit the doctor. Talk with a doctor if headaches affect your daily life. Headaches vary in how often they happen and how much pain they cause. There are more than 150 types of headaches. They fall into two main categories: primary and secondary headaches. Dysfunction or over-activity of pain-sensitive features in your head cause primary headaches. They’re not a symptom of or caused by an underlying medical condition. Common headache types have different warning signs, timing, and triggers—like tension, cluster, migraine, hemicrania continua, ice pick, and thunderclap headaches—so symptoms guide. Headache: Symptom — Overview covers definition, possible causes of this painful symptom. The International Headache Society classifies more than 150 types of headaches. More broadly, doctors recognize two categories: primary and secondary headaches. Most headaches can be treated effectively with medication, but certain instances or patterns of headache pain may be indicators or symptoms of a more serious condition.