According to the American Rhinologic Society website, various breathing allergies may affect the sense of smell by decreasing it or altering it in some way. With allergies of this type, a condition called allergic rhinitis, the change to sense of smell is temporary and returns when the allergic reaction has passed. Allergic rhinitis occurs when someone inhales an allergen, which results in itching, swelling and mucus production. This mucus prevents smells from reaching nerves higher up in the nose.
Pollen Allergies
Pollen allergies may affect the sense of smell, according to MedlinePlus, a service of the U.S. National Library of Medicine. This common allergy results from pollens, or small grains produced by plants for fertilization purposes, inhaled by someone with a sensitivity to the substance. Pollens responsible for the reaction vary from person to person but usually include trees, grasses and ragweed. The pollen triggers nasal congestion, which decreases or blocks the sense of smell.
Food Allergies
Food allergies may trigger nasal congestion, which affects the ability to sense aromas. According to MayoClinic.com, eating certain foods may trigger an immune system reaction. Food allergies affect 6 percent to 8 percent of children younger than 3, as well as about 4 percent of adults. Children may grow out of food allergies. Although severe and dangerous allergic reactions to food may occur, most present with mild symptoms, including nasal congestion that affects the sense of smell.
Pet Allergies
Approximately 10 percent of the U.S. population carries an allergy to pets, which may trigger a reaction that affects the sense of smell, according to the American College of Allergy, Asthma and Immunology website. Animal skin flakes, feathers, saliva, urine, feces and hair may cause an allergic reaction. Common pets include dogs, cats, hamsters, birds, gerbils, rabbits, mice, rats and guinea pigs; even less common pets such as goats, cows and chickens may present problems with allergies. Exposure to these animals may produce hay fever-like symptoms, which include nasal congestion and problems with smell, as reported by MedlinePlus.
