'Prolonged exposure to avian antigen present in pigeon feathers and droppings can trigger an immune response similar to that of an allergic reaction. This then causes inflammation of alveoli and bronchioles in your lungs. Left untreated, the damage to the lung tissue over time can cause what is known as hypersensitivity pneumonitis. We diagnose a lot of cases in Gujarat and this is an increasing health concern across India,' says Dr Mukesh Patel, Interventional Pulmonologist, KD Hospital, Ahmedabad.