Allergy:An inappropriate response of the immune system, which serves as the body's defense against foreign invaders like pathogens. This reaction is considered inappropriate because it targets substances that are generally harmless, known as allergens. Common examples of allergens include pollens, dust mites, molds, pet dander, and certain foods. Individuals who react to these substances are referred to as allergic or having allergies.Allergies can develop at any point in a person's life, but genetics play a significant role in the likelihood of their development. If neither parent has allergies, the probability of a child developing them is about 15%. This risk increases to 30% if one parent is allergic and exceeds 60% if both parents have allergies.Allergens trigger the production of Immunoglobulin E (IgE), an antibody present in everyone in small quantities. However, individuals with allergies produce IgE in unusually high amounts. While IgE is typically beneficial in defending against parasites, it is not meant to combat other allergens. During the sensitization phase of an allergy, IgE is excessively produced and attaches to certain cells that release chemicals, including histamine. These chemicals cause inflammation and typical allergic symptoms, illustrating how the immune system becomes misguided and reactive when exposed to an allergen.Common allergic conditions include hay fever (allergic rhinitis), asthma, allergic conjunctivitis (eye allergies), allergic eczema, hives (urticaria), and anaphylactic shock. A brief overview of each condition:Hay fever (allergic rhinitis) is the most prevalent allergic disease, characterized by seasonal symptoms due to pollen exposure. Perennial allergic rhinitis, on the other hand, is usually caused by indoor allergens like dust mites or molds. Symptoms arise from the inflammation of the nasal lining after inhaling allergens, potentially affecting nearby areas such as the ears, sinuses, and throat. Key symptoms include sneezing, nasal itching, itchy ears and throat, and post-nasal drip.Asthma involves breathing difficulties due to inflammation and spasms in the bronchial tubes, leading to narrowed air passages and restricted airflow. While often linked to allergies, asthma isn't always allergy-related. Common symptoms include shortness of breath, coughing, and chest tightness.Allergic conjunctivitis occurs when the membranes covering the eyeball and the inner eyelids become inflamed due to an allergic reaction, leading to redness, watery and itchy eyes, and swelling of the membranes.Allergic eczema is an itchy, red, or dry skin rash not usually caused by direct contact with an allergen. Symptoms include itching, redness, and dry skin, with rashes appearing on the face in children and around the eyes, elbow creases, and behind the knees in adults.Hives (urticaria) are itchy swellings on the skin that can occur anywhere on the body. They may result from an allergic reaction to food or medication, but non-allergic individuals can experience them as well. Symptoms include raised red welts and intense itching.Allergic shock (anaphylaxis or anaphylactic shock) is a severe, life-threatening reaction that can impact multiple organs. It often occurs when an allergen is ingested or injected, like certain foods or medications. The reaction is characterized by dilated and leaky blood vessels, leading to a drop in blood pressure. Symptoms may include hives, nasal congestion, throat swelling, stomach pain, nausea, vomiting, shortness of breath, wheezing, and potentially shock.
