Hay fever is like having "asthma in your nose and sinuses", according to Lung Institute of WA medical director Philip Thompson.
"It is the same conceptual approach - the same mechanisms, the same triggers that affect your lower airway can affect your upper airway," he said.
"People tend to divorce the two areas of the body and think of them as totally separate compartments but really your respiratory tract starts at the beginning of the nose and goes way down to air spaces in your lung - the alveoli."
Many of the particles people were allergic to, such as grass pollens, became trapped in the sinuses because they were too large to make their way into the lower airway, Professor Thompson explained.
"But if the same particles were able to get down into the lower airways then the same patient would probably get asthma as well."
Some patients with hay fever also have asthma. Better control of hay fever can result in better control of asthma. Professor Thompson said many people confused allergy symptoms with colds or infections.
He said most people who had a cough assumed it was related to a chest problem. "But at least one third, if not more, of the patients I see with chronic cough is due to their sinuses being inflamed or affected by allergy," he said.
"You don't need much fluid to drain off into the back of your throat to trigger a lot of coughing."