Hay fever, also called allergic rhinitis, causes cold-like signs and symptoms, such as a runny nose, itchy eyes, congestion, sneezing and sinus pressure. But unlike a cold, hay fever is not caused by a virus. Hay fever is caused by an allergic response to outdoor or indoor allergens, such as pollen, dust mites or pet dander. Hay fever can make you miserable and affect your performance at work or school and interfere with leisure activities. Hay fever symptoms may start or worsen at a particular time of year, triggered by tree pollen, grasses or weeds, which all bloom at different times. If you are sensitive to indoor allergens, such as dust mites, cockroaches, mold or pet dander, you may have year-round symptoms. Many people have allergy symptoms all year long, but their symptoms get worse during certain times of the year.