The science of migraines has always been partly cloudy.
But one thing that is clear, experts say, is that those prone to getting the throbbing headaches should be cautious over the next couple of days as the weather system that dumped snow on British Columbia and plunged Alberta into bone-chilling cold this week is about to deal a nasty blow to migraine sufferers in Ontario.
With temperatures expected to suddenly drop to a low of -6 over the weekend from today's predicted high of 16 across much of Southern Ontario, the abrupt arrival of winter will likely be a key factor in triggering some severe headaches.
"For the majority of us, we know we have to get used to the coming of winter, but for a migrainer it's almost like getting used to a different kind of weather," said David Phillips, senior climatologist at Environment Canada.
"They're like human barometers, so the change not only in pressure but temperature, humidity, wind, wind direction and air ions is going to drive them up the wall."
The roles that weather and changes in air pressure play in setting off migraines have been debated by scientists and neurologists for decades.
It has been established that barometric or temperature changes alone don't necessarily have an effect, but a combination of environmental factors and personal habits can be disastrous.
"It's a very complex issue where there's a multitude of factors and it's only the drastic weather that is visible to us, and that becomes the accused to which the finger is pointed," Mr. Phillips said.
A 2000 study out of the University of Calgary showed that Chinook winds from the Canadian Rockies -- which can raise temperatures in the region by as much as 30 degrees in a matter of hours -- are, in fact, a trigger for migraine headaches.
So a fall in temperature could very likely do the same thing, Mr. Phillips said.
But the 20-degree drop in temperature that Ontario will experience over the next two days is hardly a record, he added, and pales in comparison to the -24 C temperatures that Calgary has recently faced, or the 30 centimetres of snow Victoria and Vancouver got from the severe cold front moving down from the North.
And in January, 2005, Toronto saw a drop in temperature from 17.6 C to -10.3 C in a single day.
Valerie South, a Toronto nurse and author of the book Migraine, said she "wouldn't depict a picture of 3.2 million Canadians lying on the floor writhing and holding their heads, but the next few days could certainly be a difficult time for migraine sufferers."
Migraines are caused when blood vessels in the brain expand and press against nerves. Unlike a regular headache, a migraine may have many symptoms, including nausea, vomiting, auras, sensitivity to light and sound, numbness and difficulty in speech. Migraines are known for their severe pain and can last for days or weeks. Nearly one in five Canadians suffers from them.
Ms. South, also treasurer of the Headache Network of Canada, said the best way for migraine sufferers to avoid attacks over the next few days is to minimize their exposure to triggers they can control.
"Triggers of migraine tend to not act in isolation. They tend to gang up and it becomes the straw that broke the camel's back," she said. So if you know that red wine, chocolate or even a lack of sleep can trigger an attack, avoid them during the weather change and try to maintain a regular schedule for eating, sleeping and exercising.
"It's always better to be prepared than it is to be caught short, and right now's a good time to be sure that you're prepared."
Because the weather has been so balmy in recent days, the drop to what Mr. Phillips calls normal temperatures for this time of year will feel like a "slap in the face" for everyone.
"This drop in temperature for the collective population will not be necessarily the discomfort of a migraine, but it will still be uncomfortable because we're not prepared for it."