Symptoms include an itchy mouth, eyes or skin. Many people experience it seasonally because they are sensitive to airborne mold spores and pollens from grasses, trees and other plants. Others experience symptoms year-round, caused by environmental allergens like dust mites, pet dander (tiny scales shed from animal skin or hair) and cockroaches. However, if you are experiencing a runny or stuffy nose and a fever, you may have a sinus infection. Sinus infections are caused by bacteria or viruses, not by allergies.