@fify-- I'm not a doctor but I think that some people are just sensitive to yeast while others are truly very allergic. The symptoms can be confusing though because some experts also label mild allergies as "sensitivity."
From what I understand, those who are sensitive or only mildly allergic tend to experience fungal infections more than anything. And those who have more serious allergies develop typical allergic symptoms like swelling, hives, itching and so forth.
But in both cases, the body is unable to tolerate yeast, so the best yeast allergy treatment is avoiding yeast as much as possible.