Environmental influences... even Pam Spray can definitely be a trigger if over time the person has been exposed to chemicals long enough that some cells become very reactive to the exposure. In the PAM, it could be the propellant chemcial in the spray that is the trigger... This can occur with foods as well if, over time, one builds an intolerance to certain food components. This is not at all uncommon but what is common is for it to be unrecognized in the medical field unless you go to those who deal with toxic exposure reactions.
As Joe mentions, the pulse testing is an easy, economical assessment of potentials that cause individual reactions.
There is a classic (antique) book "The Pulse Test" by Arthur Cocoa ... that is now public domain and can be read here on the Internet... worth a look... [
empoweredsustenance.com] many options with a Google search.
Practitioners of Muscle Testing also use a battery of those tests to determine foods and substances that cause reactions in the body so they can be avoided.
When it comes to evaluating sensitivities that can cause various reactions, there are many that work and yes...they are typically outside the scope of most physicians who haven't had the extra training in the many facets of functional or restorative medicine practices.
Jackie