Respiratory allergy affects millions of people worldwide. These allergies occur when the immune system overreacts to a substance in the environment. Respiratory allergies can be caused by various environmental factors, such as pollen, dust mites, animal dander and mould spores. These allergens enter the body through inhalation and trigger an immune response that results in the release of histamine and other chemicals that cause inflammation and irritation in the respiratory system.The symptoms of respiratory allergies can vary depending on the severity of the allergic reaction. Common symptoms include sneezing, runny or stuffy nose, itchy or watery eyes, coughing, wheezing and breathlessness. In some cases, respiratory allergies can also trigger asthma attacks, which can cause severe breathing difficulties.