Although our immune system defends us from infections, it can also cause damage to our own cells and tissues. In this unfavorable situation, our immune system behaves as if it were a foreign virus attacking our bodily cells, resulting in a variety of health problems known as Allergy or Hypersensitivity.Hay fever, asthma, dermatitis, and food allergies are the most frequent allergic reactions. Allergens are chemicals that cause allergic reactions. Pollen, for example, or household dust. Mouth, nose, and skin are the entry points for allergens.Allergy symptoms vary depending on where part of the body the allergens contact. The following are a few signs and symptoms: -Coughing, itching, fever, and watery eyes.