without giving too many personal details away... my experience is that i am a nurse and a therapist. my partner, also a nurse, has an allergy which she believed for many years was one thing (and has avoided the perceived allergen), but after discussing it with myself and with the local allergy clinic, it was discovered that the allergy was something entirely different (and so had avoided the perceived allergen for no real reason). as such, she is now in the process of being desensitised to the allergen.
hope that this helps a little.