Allergy symptoms occur when your immune system overreacts to an allergen—something that usually is harmless, such as plant pollen, dust mites, molds, insect stings or food. If you have an allergy, your immune system acts as if the allergen were dangerous, releasing chemical mediators that cause allergy symptoms.
If the allergen is something in the air, your reaction will most likely affect your eyes, nose, lungs and skin. If it’s something you eat, it may affect your mouth, stomach and intestines. Food allergies also can cause skin rashes or even asthma symptoms.
Allergy symptoms will vary depending on the type of allergen.