Millions of Americans get headaches, which doctors say can signal a health problem or be problems in themselves.
Headaches can be either primary or secondary. While the pain caused by secondary headaches is a symptom of another problem -- such as a hangover, the flu, a sinus infection or in some very dangerous cases a stroke, a primary headache is a medical problem all its own.
For those who get headaches so often that they're chronic, recent studies have found that they may be caused by the very medications used to treat the pain.
People who take analgesics two or three days a week, or people who often take triptans for migraines may begin to get headaches from these medications, according to the American Headache Society.
In a large study of 160,000 people, Dr. Richard D. Lipton, a professor of neurology and director of the Montefiore Headache Center at Albert Einstein College of Medicine in New York City, found that about 2 percent of people who take medications to stop migraine pain three times a month can become dependent on the medication. They end up getting more migraines more frequently. They may need to switch medications or try other approaches to get relief from their pain.
Research suggests that more than 4 million Americans may suffer daily from medication-overuse headaches, or MOHs. Additionally, "rebound headaches" can occur when medication wears off.
Tension-type headaches are the most common headaches. Between 30 percent to 78 percent of the population experiences tension-type headaches at some time, according to the American Headache Society.
Tension type headaches are "primary" headaches -- and are often caused by stress, fatigue or sitting in one position for a long time, as when in front of a computer. They can last for as little as 30 minutes or as long as seven days, according to the American Headache Society.
"Tension headaches are often defined in opposition to migraine headaches," said Lipton.
While a migraine brings pain to one side of the head, a tension headache hurts on both sides.
"Migraine is throbbing pain. Tension headache is pressure pain, or a steady ache," said Lipton, who is former president of the American Headache Society.
Migraines are a less common but often a more debilitating type of primary headache. They can last four to 72 hours, usually affect only one side of the head and, by definition, come with other symptoms besides pain.
"The pain is always accompanied by something else -- unusual sensitivity to light, sound or nausea or vomiting, or sensitivity to movement," said Lipton.
About 60 percent of people feel nauseated with a migraine, he said, and about 20 percent of people vomit.
While the pain of a tension headache is usually "mild to moderate," migraine pain is "moderate to severe," according to Lipton.
The American Headache Society estimates that 29.5 million Americans get migraines.
Cluster headaches are the rarest and often the most severe form of primary headache. According to the American Headache Society, only about 1 percent of the population gets cluster headaches.
Migraines affect women more often than men, but men suffer more from cluster headaches.
"Hallmarks of a cluster headache are that it's short-lived, and exclusively around the eye, with symptoms around the eye," said Lipton.