Hi, your father has developed allergic rhinitis. Allergic rhinitis, commonly known as hay fever, is an allergic response to specific allergens. Some typical allergens are grass, dust, and mold. Pollen is the most common allergen. Antihistamines effectively treat allergies. They can also help prevent this condition because they block histamine formation in the body. You can use decongestants over a short period of time to help relieve stuffy nose and sinus pressure. Consult Physician....