The birds have a "fossilised" version of the key molecule responsible for severe allergic reactions in humans.
King's College London researchers say their findings, published in the Journal of Biological Chemistry, could guide the hunt for future treatments.
Experts said the work offered "exciting new avenues" for research into preventing allergies developing.
The molecule in birds, called IgY, appears to be an ancient forerunner of a similar human molecule called IgE - one of the culprits when the immune system goes into overdrive during asthma attacks or anaphylactic shock.
The King's team are trying to find out why IgE causes a problem, while IgY does not.
Dr Alex Taylor, one of the researchers, said: "This molecule is like a living fossil - finding out that it has an ancient past is like turning up a coelacanth in your garden pond.
"By studying it, we can track the evolution of allergic reactions back to at least 160m years ago."
His colleague Dr Rosy Calvert said: "We know that part of the problem with IgE in humans is that it binds extremely tightly to white blood cells causing an over-reaction of the immune system and so we wanted to find out whether IgY does the same thing."
Their lab tests revealed that it did not bind in the same way, and a more detailed comparison could reveal subtle differences which explain why, and perhaps provide targets for new drugs or treatments.
Reuters