More than 45 million Americans suffer from recurring headaches. Most of these headaches are harmless, but they can also be a symptom of a serious condition.

There are two types of headaches—primary headaches, which are not related to another condition, and secondary headaches, which are.

Primary headaches

About 90 percent of primary headaches are caused by tension. These muscle-contraction headaches cause mild to moderate pain and come and go. Tension headaches are deemed chronic if you have them more than 15 days per month.

Most tension headaches can be treated with over-the-counter pain relievers such as acetaminophen, aspirin and ibuprofen.

Migraines are another type of primary headache. The cause is unknown; however, research has demonstrated that migraines involve the actions of nerves and blood vessels. The pain from migraines is moderate to severe, and can last from hours to days. They can also be combined with stomach distress. Prescription medications are often needed to treat them. Mixed headache syndrome is a combination of tension headaches and migraines.

Cluster headaches occur one to three times per day with severe pain hitting behind one eye. Preventive medications or inhaling pure oxygen during a cluster headache may help. About 85 percent of cluster headache sufferers are male.

Secondary headaches

Secondary headaches include chronic progressive, sinus and hormone headaches.

Chronic progressive headaches worsen and become more frequent. These headaches may be caused by a brain or skull illness such as encephalitis, which is inflammation of the brain. If diseases are ruled out, doctors will try to focus on preventing the pain from striking. Preventive medication may include antidepressants or muscle relaxants.

Sinus headaches cause pain in the head and face and sometimes can fool you into thinking you have a dental problem. These headaches coincide with other sinusitis symptoms such as nasal discharge. Over-the-counter pain relievers and decongestants can help treat these headaches.

Hormone headaches come with changing hormone levels during menstruation, pregnancy and menopause, and are treated with non-steroidal anti-inflammatory drugs like ibuprofen.

Rebound headaches are caused by taking too much pain medication.

When to see a doctor

Consider seeing a doctor if you experience the following symptoms with headaches.

Headaches that began after age 50; three or more headaches per week; stiff neck; fever; shortness of breath; unexpected symptoms that affect your eyes, ears, nose or throat; dizziness; slurred speech; weakness; numbness; a tingling sensation; confusion; drowsiness; headaches that begin and persist after a head injury; a headache triggered by exertion, coughing, bending or sexual activity; a headache that intensifies and persists; headaches that change character; persistent or severe vomiting; a headache that is your “first or worst.”