An allergy is an immune system response to a foreign substance that's not typically harmful to your body. These foreign substances are called allergens. They can include certain foods, pollen, or pet dander. Your immune system's job is to keep you healthy by fighting harmful pathogens.

A sinus is a sac or cavity in any organ or tissue, or an abnormal cavity or passage caused by the destruction of tissue. In common usage, "sinus" usually refers to the paranasal sinuses, which are air cavities in the cranial bones, especially those near the nose and connecting to it.

Asthma is a chronic disease involving the airways in the lungs. These airways, or bronchial tubes, allow air to come in and out of the lungs. If you have asthma your airways are always inflamed. They become even more swollen and the muscles around the airways can tighten when something triggers your symptoms.

So, not only does having asthma increase the odds of getting a sinus infection, but a sinus infection can make your asthma harder to control. Chronic sinusitis most often is linked to nasal swelling caused by allergies, especially allergies to inhaled dust, mold, pollen, or the spores of fungi. But there's good news.