Allergies can appear as symptoms of other illnesses or medical conditions depending on the reaction. Allergic reactions to particles in the air can often manifest themselves as sneezing, nasal congestion, or a runny nose. These symptoms can be perceived as symptoms of a cold, sinus infection, or the flu. A deviated septum can also cause symptoms similar to an allergic reaction as it causes a narrowing of the nasal passage, making it difficult to breathe and disrupting the normal flow of the mucus.