Because some conditions and diseases are more debilitating than others, public health officials and policy makers have ways of defining just how disruptive and limiting each may be. One way they do this is by assessing the burden of each disease through a universal measurement called disability-adjusted life years, or DALYs. DALYs are calculated by determining the number of years a disability will cost a person and by the number of years they will experience a diminished quality of life because of the disability. 

Of the many disabling disorders categorized within this system, migraine attacks rank among the most severe. "It's a condition the World Health Organization considers the second most disabling condition on the planet in terms of DALYs," explains Dr. Robert Cowan, a board-certified neurologist and emeritus director of the headache program at Stanford Medicine. 

It can be helpful to understand what migraine headaches are and what causes them.

What is a migraine?

A migraine is a type of headache that's known for its unpredictability, severity and accompanying symptoms such as throbbing head pain, nausea and sensitivity to light and sound. "A few people also experience a migraine ‘aura’ of bright visual symptoms that last around an hour, but most people experience the 'sick' form of the headache," explains Dr. Anne MacGregor, a headache and women's health specialist at the Centre for Neuroscience, Surgery and Trauma in London. 

Many migraine symptoms are debilitating enough that it becomes difficult or impossible for the affected person to carry out even routine daily activities. "Migraine attacks can have a substantial impact on a person’s life and it’s not uncommon for someone to share that they’ve had to miss out on important life events, turn down opportunities or have had relationships negatively impacted because of them," says Rashmi Halker-Singh, a neurologist and director of the headache medicine fellowship program at Mayo Clinic in Arizona.

How are migraine attacks different than headaches? 

Some people think of a migraine as being different than a headache, but the reality is that a migraine is simply one of many different types of headache. "There are over 300 different causes of headache," explains Halker-Singh, "and a migraine is just one specific headache diagnosis."

Another way of thinking about the difference between the two is that a headache is literally any form of ache or pain experienced in one's head, while the pain associated with a migraine is usually a more acute and severe pain while also being accompanied by the other aforementioned debilitating symptoms. Also unique is that unlike most headaches, "migraine attacks often don’t respond to simple painkillers," says MacGregor. 

Specific conditions must be met for a headache to be defined as a migraine. "A migraine diagnosis is made when a person has at least 5 lifetime attacks of headache or head pain that meets certain criteria," says Halker-Singh. These include one's pain lasting at least 4 hours without treatment and at least 2 of the following 4 features: the pain is more intense on one side of one's head; it throbs or pulsates; it's moderate to severe in intensity; and it worsens with activity. Additionally, individuals need to experience either nausea or a sensitivity to lights and sounds during the migraine. "By asking a lot of detailed questions about the headache, we can determine if the person has a diagnosis of migraine," say Halker-Singh.

What causes migraine attacks?

Migraine attacks are believed to have several causes or contributing factors, but research is still ongoing to better understand some of them. One area that has been well studied is the part genetics play. "In the most basic of terms, migraine is considered a genetic disorder," says Halker-Singh. She says this is true even if you can’t identify a family member who has experienced a migraine because "the genetics are a bit complex" and can affect one person without affecting another.

Another contributing factor is that individuals who are hypersensitive to any general stimulating factor may experience migraine attacks more frequently. "People prone to experiencing a migraine often tell us that they are generally much more aware of bright lights, sounds and smells compared to people they know who don’t experience migraine attacks," says Macgregor. 

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It's also possible that nothing significant has actually caused the migraine and that it's the result of a threat that isn't really there. “The main job of the brain is to help one survive by warning of potential threats from the environment - both the internal and the external," explains Cowan. He says that for some people who experience migraine attacks, their brain may recognize that something minor is wrong such as a skipped meal, bad food, disrupted sleep or an unexpected physical exertion, and then "sound an alarm to get away from that situation," something it does "with pain, nausea, and driving patients to a cool, dark, quiet place it associates with safety."

Regardless of what causes them, migraine attacks can be both uncomfortable and inconvenient; but it's fortunately a common condition that has many treatment options available.

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