Final answer:
Hypersensitivity, such as an allergy, arises when the immune system overly reacts to harmless substances called allergens. Symptoms of allergies can include sneezing, itchy eyes, and rashes. The most serious reaction is anaphylaxis, and common allergens involve plant pollens, dust mites, specific foods, and some medications.
Step-by-step explanation:
An allergy is a hypersensitivity of the immune system to typically harmless substances in the environment, known as allergens. These allergens can include plant pollens, dust mites, mold, pet dander, insect stings, certain foods such as peanuts and shellfish, or medications like aspirin and penicillin. Allergens can be inhaled, ingested, or come into contact with the skin, leading to symptoms such as sneezing, a runny nose, itchy eyes, or an itchy rash. Food intolerances and food poisoning, while they may cause similar symptoms, are not the same as a hypersensitivity allergy.
The most severe form of allergic reaction is anaphylaxis, which can be life-threatening and requires immediate medical attention. Other allergic conditions include hay fever, eczema (atopic dermatitis), and allergic asthma. These conditions are the result of an immune response involving the production of IgE antibodies and the sensitization of mast cells, leading to an inflammatory response upon subsequent exposures to the allergen.
Common examples of allergic skin diseases include allergic contact dermatitis, often caused by skin contact with irritants such as poison ivy, and urticaria (hives). Reactions to these allergens vary in severity and can be managed through avoidance, medication, or allergy immunotherapy in some cases.