The symptoms of seasonal allergy include runny nose, repetitive sneezing, and itching in the eyes, nose throat or roof of the mouth. Prolonged allergy symptoms include nasal congestion, fatigue, irritability and dark circles under the eyes, among other things. Food allergy symptoms appear within 2 hours of eating, and can be life-threatening. Key symptoms include hives, hoarse voice and wheezing. Other symptoms that can occur are swelling, itching around the mouth, nose and throat, difficulty swallowing, stomach cramps, etc. Severe reactions can even cause low blood pressure and blocked airways.