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Find out what you are allergic to. Avoid triggers. Cover your face. Wash your hands frequently. Wash your face after coming into contact with allergens.
A doctor can run an allergy test, which will help narrow down and even pinpoint exactly what allergen you are suffering from. Sometimes, they come back inconclusive or will indicate several allergies. The more information you can gather about your allergy, the better. Once you have a general idea of what causes your runny nose, you can start avoiding exposure to those allergens. Environmental irritants and allergens like pollen, pet dander and hair, dust, and cigarette smoke can all dry out nasal passages and start the runny nose cycle. Use an air purifier in your home to remove these irritants from the air, but recognize that it is virtually impossible to avoid all triggers unless you seal yourself inside an air-tight container.  One of the most common airborne allergens in the United States is ragweed pollen, and there are over 17 varieties. Although it is almost impossible to avoid exposure to ragweed completely, you can learn where high concentrations are likely to be located in your local environment. Avoid these locations as best you can. Avoid going outside during peak times, such as early morning, and close your windows when pollen counts are high. Reduce dust mites in your home by minimizing the presence carpeting, blankets, and stuffed animals. Use dust mite covers for mattresses and pillows. This is probably the most extreme way to protect yourself from the allergens that produce a runny nose. If the particles can’t get into your body, they can’t cause a runny nose. If you go outside during allergy season, wear a scarf over your nose and mouth. A protective face mask can do an even a better job. This will prevent allergens from spreading. Use soap and water. Any soap will work because you are only trying to remove allergens, not kill bacteria. Scrub your hands for at least 20 seconds. Rinse and dry your hands on a clean towel. If you are allergic to pet dander, wash your face after petting a dog. If you are allergic to pollen, then wash your face when you come indoors after being outdoors for a while. This will help reduce your exposure to allergens.