Allergies (Hypersensitivity)

Allergies (Hypersensitivity):

• Some of the individuals are very sensitive to some particles present in the environment.
• The exaggerated response of the immune system to certain antigens present in the environment is called allergy (allo-altered, erg-reaction).
• The substances to which such an immune response is produced are called allergens.
• The common examples of allergens are mites in dust, pollens, and some proteins in insect venom.
• An allergen is an antigen that causes an allergic reaction.
• Allergy is a form of an overactive immune response mediated by IgE and mast cells.
• Allergy is due to the release of chemicals like histamine and serotonin from the mast cells.
• Symptoms of allergic reactions include sneezing, watery eyes, running nose, and difficulty in breathing.
• For determining the cause of the allergy, the patient is exposed to or injected with very small doses of possible allergens, and the reactions are studied. 
• The use of drugs like anti-histamine, adrenalin, and steroids quickly reduces the symptoms of allergy.
• Allergic reactions begin within a few seconds after the contact with the allergen and last about half an hour.
• Hay fever and asthma are some common examples of allergies.
• Anaphylaxis is the classical immediate hypersensitivity reaction. It is a sudden, systematic, severe, and immediate hypersensitivity reaction occurring as a result of rapid generalized mast-cell degranulation.