Triggers, which vary in all aspects, are things and/or events that lead
to the activation of a headache. For example, what initiates a headache
for a certain person many not get the same result from someone else. Furthermore,
a person might receive a headache from a certain trigger at one point
yet that same trigger might not have the same effect a second time. "In
fact, what triggers a migraine for one sufferer may actually help prevent
it in another," says the Migraine Relief Society at http://headaches.about.com/gi/dynamic/offsite.htm?site=
This could also be applied to headaches.