Allergy is the disease related with the immune system that overreacts to substances called allergens. Allergies are categorised on the basis of the time of the year they appear or the part of the body that they affect or on the basis of its triggers. Allergy can be caused by anything like food, pollen, latex or insects.

Some allergies are manifest during a particular time of the year only. Theses allergens enter the body through nose, mouth or absorbed by the skin. Some allergens get injected into the body too like insect sting and needles while administering injectable drugs.