I think people equate a Sensitivity as Allergy. But then we can go back and forth forever on the definition of Sensitivities and Allergies
The only thing that is accurate, if you do have either a sensitivity or an allergy to a liquid, it could be a number of things that is causing the issue. The only ways to determine what it is, is to see a doctor and/or take all things away from the equation and slowly introduce the products (one by one) back into the equation.
Start with unflavored, either a pg
or vg mix. Vape that for a few days. Introduce the next ingredient. So on and so forth. Sometimes it is as simple as a flavor or flavor company that doesn't agree with you.
It is all trial and error. Even when you go to a doctor, it is trial and error. The best a doctor can do are the spot tests to determine if a particular substance causes a reaction. Better to know though.