It's important to know what's causing your symptoms because treatment depends on the type of nasal inflammation. Some of the most important causes of nonallergic nasal inflammation, also called nonallergic rhinitis, include the following:

Irritants. Fumes, weather changes, emotional stress, and other factors can cause vasomotor rhinitis, or irritant rhinitis. These symptoms are similar to those of nasal allergies but aren't caused by allergy or infection. Even certain medications, such as the high blood pressure medicines reserpine and prazosin, can result in the stuffy or runny nose of vasomotor rhinitis. Often the cause is not known. While doctors aren't sure exactly why some people develop vasomotor rhinitis reactions, they know the blood vessels in the lining of the nose appear to be extra sensitive and swell up in response to irritants. Vasomotor rhinitis is more common in adults than in children.

Eosinophils. These are special blood cells that are part of the immune system. They are sometimes called "allergy cells." They can play a role in nasal allergies, but large numbers are also present in people with nonallergic rhinitis.

Neutrophils. Like eosinophils, neutrophils are a type of blood cell. They seek out and destroy harmful substances in the body. As they do their work, they may trigger a stuffy nose and other symptoms. Most often, they're present in large numbers during sinus infections.

Structural problems. Problems with your nose structure may cause nasal inflammation. For instance, chronic inflammation from injury can cause allergy-like symptoms. Another cause is incorrect growth of the cartilage between your nostrils, called the septum. Nose injuries often result in a deviated septum, in which the partition of bone and cartilage that divides the nose is pushed to one side or the other, narrowing the passageway on one side. If the passageway is very narrow, it can cause breathing problems and block the normal flow of mucus.

Cold or flu. Viruses that cause colds and flu start a defensive inflammatory reaction that results in a runny or stuffy nose, sneezing, and watering eyes. These symptoms can be indistinguishable from allergy symptoms.