If you have a food allergy, it means that your body doesn't identify certain proteins properly. The food that you're allergic to contains proteins that your immune system has accidentally flagged as dangerous. Once your body thinks that food is bad for you, it will react every time you eat it. Its reaction is to release an antibody called immunoglobulin E to fight off the protein, or allergen. The antibody then sends out a team of chemicals to attack the allergen. One of these chemicals is called histamine, and it's responsible for many of the symptoms that your allergy causes.
If one of your food allergy symptoms is nasal congestion, spicy food can act as a natural remedy for that problem. Spicy foods can thin the mucous you're secreting and clear blocked nasal passages. The spicier the food, the better it may be for your allergy. Recommended spices for clearing your congestion include cayenne pepper, hot ginger, fenugreek, onion and garlic.