One whiff of a plant known as the headache tree can spur intense, excruciating pain — and now scientists know why.  an ingredient in the tree sets off a chain of events that eventually amps up blood flow to the brain’s outer membrane.

Other headache triggers, such as chlorine, cigarette smoke and formaldehyde, interact with some of the same cellular machinery, suggesting they all work via the same pain-inducing mechanism.

In the new study, an international group of researchers extracted the plant compound umbellulone from dried bay laurel leaves and then exposed various mouse and rat cells to the compound.  Umbellulone tickles the same cellular detector that responds to painfully cold stimuli and the sinus-clearing scent of wasabi and mustard oil, the researchers report online October 27 in Brain.

Stimulating this chemical detector ultimately triggers the release of a particular protein implicated in migraine headaches, the researchers found. This protein prompts blood vessels to swell, and scientists think this swelling puts pressure on the skull and nerves, causing pain.

The new research is solid, says neuroscientist Peter Goadsby, director of the headache center at the University of California, San Francisco. other irritants linked to headaches interact with the same chemical detector, and it may be a good target for therapy, Goadsby says.

The scent of the bay laurel tree, Umbellularia californica, had been anecdotally implicated as a headache trigger, but it took a self-experimenting headache-sufferer to bring the plant to the attention of researchers in the Headache Center at the University of Florence. Pierangelo Geppetti, who led the study, heard from a friend about a man who was trimming trees on his property and suddenly experienced a cold sensation in his left nostril and then excruciating pain around his left eye. in his youth, the man had regularly gotten cluster headaches, which are one-sided, intense bouts of exceptional pain that often recur in people who suffer from them.

Unlike a full-bore cluster headache, the man’s symptoms quickly faded, and he forgot about the episode. but a few months later when he was again working with bay laurel, the headache struck again.  This prompted him to experiment, intentionally sniffing the crushed leaves of the tree. the intense pain resumed and not long after, Geppetti heard the headache story from their mutual friend.  Intrigued, he began investigating the chemical compounds that might be responsible.

found in: Body & Brain and Molecules