Final answer:
An allergy is an immune reaction to harmless environmental proteins called allergens, leading to symptoms that range from mild to severe. The underlying cause is a hypersensitive immune system, often with genetic predispositions that can make some individuals more prone to allergies.
Step-by-step explanation:
Allergies: An Immune System Reaction
An allergy is an immune disorder characterized by an excessive response to a typically harmless antigen, known as an allergen. The immune system's hypersensitivity to such allergens can range from mild symptoms like sneezing and itchy eyes to more severe reactions, including anaphylaxis. Allergies are more prevalent in children, with some outgrowing them as they reach adulthood. Genetic factors also play a role, as the likelihood and severity of allergies can increase if one's parents are allergic.
There are different types of hypersensitivities associated with allergies. Type I hypersensitivity, for example, involves mast cells and the production of IgE antibodies upon first exposure to an allergen. During subsequent exposures, these antibodies can cause mast cells to release inflammatory mediators like histamine, leading to allergic symptoms. Allergens may enter the body through inhalation, ingestion, or skin contact, with common sources including pollen, dust mites, animal dander, insect stings, and certain foods and medications.
Common Symptoms and Allergic Conditions
Some common allergic conditions are hay fever, food allergies, atopic dermatitis, and allergic asthma. Symptoms like red eyes, an itchy rash, sneezing, a runny nose, or swelling are typical of allergic reactions. It's important to distinguish between allergies and other conditions like food intolerance, which do not involve an immune response.