Allergies are caused by the immune system’s reaction to things in our environment. The things you are allergic to are called allergens. Allergens can range from the things such as pollens and molds to food and chemicals. By far the allergens that cause the most sinus problems are those that we inhale such as pollens and molds.
When the body comes into contact with something to which it is allergic, it produces histamine, a chemical that causes swelling and inflammation. If allergies are severe and persistent enough, chronic conditions such as rhinitis, sinusitis, or asthma can result.