Bird Breeders Lung is a disease that is caused over time by the accumulation of particulate (in this case feather dust etc) in the lungs which causes the lungs to not be able to perform their functions with regard to breathing.
ALLERGIES are an immediate reaction - usually mediated by one of our bodys' natural chemicals, HISTAMINE, in the body BUT NOT ALWAYS - to a substance or irritant. An allergicv reaction CAN result in swollen airways (ie asthma or other type of non-breathing reaction) or swollen neck lips face etc, OR sinus-type reactions (ranging from mild to equivalent of a VERY VERY BAD cold), EYE irritation, headaches, skin irritation, etc.
When mediated by the body's histamine process, ALLERGIES can be alleviated to various extent by use of anti-histamines, and full remission occurs with time and avoidance of all allergens.
Bird Breeders Lung, as a particulate-caused disease, will not be helped by antihistamines and is more-or-less a chronic & progressive disease by the time it has occurred. Not really reversible, and occurrs over time of long exposure.