Flying is a headache for many people, but for some that figure of speech becomes literal with "airplane headache," a form of pain that flares up during landing, researchers said.
The unusual, specific head pain - severe usually on one side of the head and near the eye - was first reported in medical literature in 2004, with several dozen more cases documented in the following years.
Now, Italian researchers writing in the journal Cephalalgia argue that "airplane headache" should be considered a new subtype of headache and suggest a list of criteria doctors can use to diagnose it.
"The 'headache attributed to airplane travel,' also named'airplane headache,' is a recently described headache disorder that appears exclusively in relation to airplane flights, in particular during the landing phase," wrote lead researcher Federico Mainardi, of Giovanni e Paolo Hospital in Venice.
Mainardi's group describes the cases of 75 people with symptoms suggestive of airplane headache. Those individuals had contacted the doctors after reading about airplane headache in a piece Mainardi published in 2007.
Researchers had all of them complete detailed questionnaires to describe their symptoms. Overall, they fit the features of past cases of airplane headache: severe pain on one side of the head that was usually limited to the time the plane was landing.
The headache was almost always short lived, less than 30 minutes for 96 per cent of the people. Only a minority consistently had headaches during landings, and for most it happened on some flights but not on others.
"Is (airplane headache) a unique disorder? I think it is. But others might disagree," said R. Allan Purdy, a neurologist and professor at Dalhousie Medical School in Halifax, Canada, who wrote an editorial on the report.
"Nobody knows what causes it. Nobody knows how many people have it. Nobody knows what treatments work," he added, but noted that classifying it as a distinct disorder would allow it to be studied more directly.
There were limitations to the report, including the fact that nearly all the individuals involved were assessed long-distance, without a physical exam.
It's not clear what might trigger the headaches. One theory is that the pain may be related to pressure changes in the sinus cavities, based on the idea that passengers with colds or sinus infections can get severe headaches during take-off or landing.
Another question is why only some passengers get them. But Purdy said that over half the people in the current report also had a history of other headache problems including migraines and frequent tension headaches.
Mainardi's team says airplane headache is distinct from migraines and other well-known headache types.
One of their diagnostic criteria is that the pain can't be linked to other causes. They also say a person should have had at least two attacks of severe head pain during flight, with the symptoms lasting no more than 30 minutes, and there shouldn't be any other symptoms, such as nausea or sensitivity to light or noise, that may be signs of migraine.
The good news is that airplane headache seems harmless.
"It doesn't appear to be a serious or life-threatening disorder," Purdy said.