The altered reactivity of a sensitized individual on exposure to an allergen.
A hypersensitivity state induced by exposure to a particular antigen (allergen) resulting in harmful immunologic reactions on subsequent exposures. The term is usually used to refer to hypersensitivity to an environmental antigen (atopic allergy or contact dermatitis) or to drug allergy.
Hypersensitivity, or overreaction, to substances such as drugs, food, and pollen. Allergies are sometimes very difficult to predict and prevent.
Hypersensitive reaction, such as wheezing or a rash, to a foreign substance that stimulates the immune system.
An unusual sensitivity to some substances such as pollen or dust, which cause a physical reaction such as sneezing or a rash in someone who comes into contact with them.
A condition in which body tissues of sensitive people react to specific allergens, while those of non-sensitive people do not. The response is histamine mediated. The reaction can be mild, moderate, or severe depending on the sensitivity of the individual. Symptoms can include headache, urticara, eczema, rash, asthma, hay fever, hemorrhage, gastrointestinal disturbances, nausea, vomiting, and in rare instances, circulatory collapse, shock, and death.
An excessive response by the immune system to some foreign substance, called an antigen or, more specifically, an allergen. Allergy is a general term that encompasses a wide range of problems, including asthma, reaction to food additives, and some kinds of food intolerance (all treated in separate entries), as well as hypersensitivity to many other substances such as pollen, mold spores, insects, insect bites, animal der, and injected drugs, such as penicillin. Why some people suffer from allergies and others do not is unclear, but some sensitivities seem to be inherited.
Hypersensitivity to proteins, drugs or bacterial or viral substances, as a result of contact as opposed to an inherited tendency. Allergic and related conditions are compared under the heading hypersensitivity.
Hypersensitivity reaction to the presence of an agent (allergen) that is intrinsically harmless, such as animal hairs, dust, pollen, or substances in certain foods. Symptoms vary widely but may include bronchial congestion, the appearance of a rash (often itchy), vomiting, edema, conjunctivitis, runny nose, and swelling of the eyes and nares or serious systemic reactions leading to anaphylactic shock and possibly death. Allergies are very common, affecting probably more than 15% of the U.S. population. Allergies are diagnosed through skin tests (patch test, scratch test) and other laboratory procedures. Treatment is avoidance of the allergen, if possible; the use of antihistamine drugs to relieve the symptoms, desensitizing injections in some cases (e.g., hay fever), and other measures.
A disorder in which the body becomes hypersensitive to particular antigens (called ‘allergens), which provoke characteristic symptoms whenever they are subsequently encountered, whether inhaled, ingested, injected, or otherwise contacted. Normally antibodies in the bloodstream and tissues react with and destroy specific antigens without further trouble. In an allergic person, however, the reaction of allergen with tissue-bound antibody (reagin) also leads, as a side-effect, to cell damage, release of ‘histamine and ‘serotonin, inflammation, and all the symptoms of the particular allergy. Different allergies afflict different tissues and may have either local or general effects, varying from asthma and hay fever to severe dermatitis or gastroenteritis or extremely serious shock.
An acquired condition of the body so that it reacts abnormally to a chemical substance or physical agent, such as cold. The term is also applied to the branch (specialty) of internal medicine dealing with the study, diagnosis, and treatment of allergic disorders.
A term generally used to describe an adverse reaction by the body to any substance ingested by the affected individual through the lungs, stomach, skin or mucous membranes (such as the lining of the eye). Strictly, allergy refers to any reactions incited by an abnormal immunological response to an allergen, and susceptibility has a strong genetic component. Most allergic disorders are linked to ATOPY, the predisposition to generate the allergic antibody immunoglobulin E (IgE) in response to common environmental agents. Because IgE is able to sensitise mast cells (which play a part in inflammatory and allergic reactions) anywhere in the body, atopic individuals often have disease in more than one organ. Since the allergic disorder hay fever was first described in 1819, allergy has moved from being a rare condition to one afflicting almost one in three people in the developed world, with substances such as grass and tree pollen, house-dust mite, bee and wasp venom, egg and milk proteins, peanuts, antibiotics, and other airborne environmental pollutants among the triggering factors. Increasing prevalence of allergic reactions has been noticeable during the past two decades, especially in young people with Western lifestyles.
An immune response to a foreign antigen that results in inflammation and organ dysfunction. Allergies range from life-threatening to annoying and include systemic anaphylaxis, laryngeal edema, transfusion reactions, bronchospasm, vasculitis, angioedema, urticaria, eczematous dermatitis, hay fever, rhinitis, and conjunctivitis. They affect about 20% of the American public and can be triggered by inhalation (e.g., pollens, dust mites), direct contact (e.g., poison ivy, poison oak), ingestion (e.g., drugs, foods), or injection (e.g., stinging insects, drugs). Allergic responses may be initiated and sustained by occupational exposures to allergens, and by foods, animals, fungal spores, metals, rubber products, and other agents. The most severe cases are often associated with Hymenoptera stings, penicillin products, radiological contrast media, and latex.
A reaction by the body’s immune system to a harmless substance.
Reaction due to extreme sensitivity to certain foods, chemicals, or other normally harmless substances.
In the realm of the human immune system, a remarkable response unfolds when the body encounters certain environmental substances. This response, known as an allergic reaction, manifests as a collection of symptoms that encompass the appearance of a rash, localized inflammation, bouts of sneezing, the sensation of itchy and watery eyes, a runny nose, and even irritations of the skin.
Allergic diseases encompass a range of conditions that arise due to abnormal or heightened immune responses to diverse substances called allergens. Numerous prevalent ailments, including asthma and hay fever, result from allergic reactions to substances that typically do not cause symptoms in the majority of individuals.
Allergic reactions manifest only upon subsequent encounters with an allergen, following initial sensitization of the body during the first exposure. The exact reasons why certain individuals develop allergies remain unclear; however, approximately one out of every eight people appears to possess an inherited inclination towards them.
The primary role of the immune system is to identify foreign proteins called antigens found on the surfaces of microorganisms and generate antibodies (also known as immunoglobulins) and sensitized lymphocytes (a type of white blood cell). Upon subsequent encounters with these antigens, the antibodies and sensitized lymphocytes engage with them, resulting in the elimination of the microorganisms.
In allergies, a comparable immune response takes place, with one key distinction: the immune system generates antibodies or sensitized lymphocytes against harmless substances. This occurs due to the misidentification of allergens as potentially harmful antigens.
The excessive or disproportionate reactions observed in allergies are referred to as hypersensitivity reactions, which can manifest through four distinct mechanisms categorized as Types I to IV hypersensitivity reactions.
The most widely recognized allergies are attributed to Type I hypersensitivity, also known as anaphylactic or immediate hypersensitivity. In this type of hypersensitivity, allergens prompt an immediate immune response by stimulating the production of specific antibodies called immunoglobulin E (IgE). These IgE antibodies coat cells known as mast cells or basophils, which are present in the skin, stomach lining, lungs, and upper respiratory airways. Upon subsequent exposure to the allergen, it binds to the IgE antibodies, triggering the release of various chemicals from the granules within mast cells. These chemicals are responsible for the allergy symptoms experienced by individuals.
One of the chemicals released during Type I hypersensitivity reactions is histamine, which leads to the dilation of blood vessels, fluid leakage into tissues, and muscle contraction, particularly in the airways of the lungs. Symptoms associated with this type of reaction may include itching, swelling, sneezing, and wheezing. Type I hypersensitivity is linked to various conditions such as asthma, hay fever, urticaria (nettle rash), angioedema, anaphylactic shock (a severe, widespread allergic reaction), and possibly atopic eczema and certain food allergies.
Types II to IV hypersensitivity reactions, characterized by distinct mechanisms compared to Type I reactions, are less frequently associated with allergies. However, contact allergic dermatitis, which occurs when the skin reacts to prolonged contact with substances like nickel, is attributed to a Type IV hypersensitivity reaction.
Whenever feasible, the most efficient approach to treating any form of allergy is to avoid exposure to the specific allergen in question.
Pharmacological treatment for allergic reactions involves the administration of antihistamine medications, which help alleviate the associated symptoms. Certain antihistamines possess sedative properties, making them beneficial for addressing nighttime itching caused by eczema. Conversely, many antihistamines do not induce drowsiness, rendering them more suitable for daytime usage.
Medications like sodium cromoglicate and corticosteroids can be employed on a regular basis to proactively prevent the development of symptoms.
Hyposensitization, which can be beneficial for a small portion of individuals experiencing allergic reactions to particular allergens like bee stings, involves a treatment approach where the allergen doses are gradually increased. This process aims to stimulate the production of antibodies that can effectively inhibit future reactions. However, it is crucial to conduct hyposensitization under close medical supervision due to the potential risk of severe allergic reactions.
Few words are as commonly misused as this one. People often claim to have allergies when they actually mean they are hypersensitive to specific substances. To accurately define it, allergy is “a condition that arises when certain substances, typically of a protein nature, are introduced into the body and trigger a complex disease known as an allergy.” This can manifest in various ways, such as asthma, hives (urticaria), or certain skin disorders. The allergen responsible could be something in the environment, like pollen from plants causing hay fever, something in the diet, like eggs or fish leading to asthma, or something that comes into contact with the skin, resulting in allergic dermatitis. This last type is often linked to an overly sensitive nervous system.
A condition of heightened sensitivity triggered by exposure to a specific antigen (allergen), leading to harmful immune responses upon subsequent exposures.
An exaggerated reaction to a particular substance, commonly pollen, resulting in itching and swelling.