Difference btwn an allergy and sensitivity? I get hay fever symptoms every time I visit the salon. I think it is due to an ingredient in the shampoo.

Sensitivity. You can get allergy like symptoms from both allergic and nonallergic causes. Most likely your sensitivity to the chemicals in the air at the salon is nonallergic. That being said, if you have allergies to things like pollens and dust mites then your eyes and nose will be more "sensitive" or more easily irritated by those chemicals in the air. Allergy is a very specific kind of sensitivity.