• Your sinuses may react to an allergen, such as pet dander, dust, dust mites, pollen, or any other tiny particle you are allergic to, and your immune system will attack it and cause your nasal membranes to swell up and
block your sinuses. In the case of pollen, it could be seasonable. A food allergy
can also cause this condition. The discharge that results from this is usually clear or whitish.
• A fungus, including mold, can settle in the nose and cause chronic sinusitis.