People experience allergies when their immune system views a foreign object, otherwise known as an allergen, as a harmful substance. The system overreacts, sending a type of chemical mediator called histamines, to get the body to release allergens from your system. This is why you sneeze, cough, and itch when you experience an allergic reaction. It's your body's way of telling you that something that has come in must go out. Allergic reactions can range from mild to severe and be triggered by all sorts of allergens. The most common symptoms of an allergic reaction include: Watery eyes
Runny nose
Nasal congestion
Sneezing
Itchy eyes and nose
Rashes or hives
Swelling, particularly around the eyes, lips, and face, as well as the tongue
Pain and redness, especially for bites and stings
Coughing, a scratchy throat, and a feeling of one's throat closing