Allergy
In 1906, a Viennese pediatrician named Clemens von Pirquet observed something strange in his patients. Children who had received injections of horse serum or smallpox vaccine reacted with quicker and more severe symptoms upon their second exposure to the same substance. He coined the word allergy from the Ancient Greek terms allos meaning other and ergon meaning work to describe this phenomenon. An allergic reaction occurs when the immune system mistakenly identifies an ordinarily harmless allergen as a threat. This exaggerated response triggers the release of inflammatory chemicals such as histamine from mast cells or basophils. Symptoms can range from red eyes and sneezing to life-threatening swelling known as laryngeal edema. The body produces immunoglobulin E antibodies that bind to these specific receptors on immune cells. When the allergen appears again, it cross-links with the IgE molecules held on the surface of the mast cells. This activation causes degranulation where granules release histamine and other mediators into surrounding tissue. The result is vasodilation, mucous secretion, nerve stimulation, and smooth muscle contraction.
Pollen, certain foods, metals, insect stings, and medications represent common allergens found in daily life. Airborne particles like dust mite droppings trigger reactions in areas exposed to air such as the nose, eyes, and lungs. Allergic rhinitis causes irritation of the nasal mucosa leading to runny noses and sneezing. Inhaled allergens increase mucus production in the lungs causing shortness of breath and wheezing. Food allergies often manifest as abdominal pain, bloating, vomiting, and diarrhea rather than respiratory issues. Skin contact with substances like latex results in dry crusted lesions lasting 48 to 96 hours. A large local reaction from an insect sting may create skin redness greater than 10 centimeters in size. Systemic allergic responses called anaphylaxis can affect multiple organ systems including digestion and circulation. These severe reactions include low blood pressure, coma, and potentially death if untreated. Approximately 25% of the population develops a strong immune response to urushiol found in poison ivy plants.
Identical twins share the same allergic diseases about 70% of the time while non-identical twins show this trait only 40% of the time. Heredity remains the most significant host factor influencing allergy susceptibility across generations. However genetic factors alone cannot explain the rapid rise in allergic disorders seen since industrialization began. Four major environmental candidates drive these changes: alterations in exposure to infectious diseases during early childhood, environmental pollution, high allergen levels, and dietary shifts. The hygiene hypothesis suggests that insufficient stimulation of the TH1 arm of the immune system leads to overactive TH2 responses. Children living in too sterile environments lack enough pathogens to keep their immune systems busy. This imbalance causes normally benign objects like pollen to trigger dangerous immune attacks. Studies show that various immunological and autoimmune diseases are much less common in developing nations compared to industrialized ones. Immigrants to developed countries increasingly develop these disorders based on how long they have lived there. Longitudinal data from third-world countries demonstrate rising immunological issues as nations grow more affluent and cleaner.
Skin prick tests involve tiny punctures made into a patient's skin using small plastic or metal devices. Allergens such as pollen grass mite proteins or peanut extracts are introduced to marked sites on the inside forearm or back. A visible inflammatory reaction usually appears within 30 minutes ranging from slight reddening to full-blown hives called wheal and flare. Interpretation by well-trained allergists occurs on a scale where plus-minus means borderline reactivity and four-plus indicates a large reaction. Blood testing measures specific IgE antibody concentrations without exposing patients to any allergens during the procedure. An allergy blood test is available through most laboratories and sends samples for analysis with results returned days later. The RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics AB in Uppsala Sweden. In 1989 this company replaced it with a superior test named ImmunoCAP Specific IgE blood test using fluorescence-labeled technology. Challenge testing introduces tiny amounts of suspected allergens orally or via inhalation but requires close supervision by an allergist. Elimination challenge tests instruct patients to avoid an allergen completely before reintroducing it to see if symptoms return.
Antihistamines glucocorticoids epinephrine mast cell stabilizers and antileukotriene agents form common treatments for allergic diseases. Severe life-threatening anaphylaxis often requires immediate injection of epinephrine which may be delivered via autoinjector devices when medical care is unavailable. Allergen immunotherapy exposes people to larger and larger amounts of allergen to change immune system responses over time. Meta-analyses found that injections under the skin effectively treat allergic rhinitis in children and asthma with benefits lasting years after stopping treatment. Sublingual immunotherapy gives allergens under the tongue though evidence supports its use less strongly than injections. Early exposure to peanut products has greatly reduced peanut allergies among young children in the United States following revised guidelines from 2015 and 2017. Researchers observed a 43% drop in frequent occurrence of peanut allergies preventing an estimated 40,000 cases. Fish oil supplementation during pregnancy associates with lower risks of food sensitivities while probiotic supplements may help prevent atopic dermatitis. Saline nasal irrigation and butterbur show relatively strong effectiveness compared to other alternative medicine treatments like honey or acupuncture.
Allergic diseases including hay fever and asthma have increased in the Western world over the past two to three decades. Increases in allergic asthma began in the 1960s and 1970s with further rises occurring during the 1980s and 1990s. In the United States about 35.9 million people suffer from allergic rhinitis representing roughly 11% of the population. Asthma prevalence increased 75% from 1980 to 1994 affecting approximately 10 million Americans. Atopic eczema affects about 9% of the US population while its prevalence rose from 3% to 10% in children between 1960 and 1990. Anaphylaxis causes at least 40 deaths per year due to insect venom and around 150 annual fatalities from food allergy. A 117.3% increase in peanut allergies was observed from 2001 to 2005 affecting an estimated 25,700 people in England alone. Multiple allergies combining asthma eczema and allergic rhinitis affect 2.3 million people showing a 48.9% rise between 2001 and 2005. Rates of many allergic diseases appear to be increasing globally though new cases remain much lower in developing countries.
Some symptoms attributable to allergic diseases are mentioned in ancient sources involving three members of the Roman Julio-Claudian dynasty including Augustus Claudius and Britannicus. The concept of allergy was originally introduced in 1906 by Clemens von Pirquet after he noticed rapid severe reactions to second injections. All forms of hypersensitivity used to be classified as allergies thought to result from improper activation of the immune system. In 1963 Philip Gell and Robin Coombs designed a new classification scheme describing four types of hypersensitivity reactions known as Type I through Type IV. With this framework the word allergy became restricted to type I hypersensitivities characterized as rapidly developing reactions involving IgE antibodies. A major breakthrough occurred when immunoglobulin E was simultaneously discovered in 1966-67 by Ishizaka's team at the Children's Asthma Research Institute and Hospital in Denver USA. Gunnar Johansson and Hans Bennich in Uppsala Sweden also identified this antibody class independently. Their joint paper was published in April 1969 marking a pivotal moment in understanding allergic mechanisms. The medical specialty studying these conditions is called allergology requiring physicians to complete at least nine years of training.
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Common questions
Who coined the word allergy and when did this happen?
Clemens von Pirquet coined the word allergy in 1906 after observing rapid severe reactions to second injections of horse serum or smallpox vaccine. He derived the term from Ancient Greek words allos meaning other and ergon meaning work.
What is the biological mechanism behind an allergic reaction involving IgE antibodies?
The body produces immunoglobulin E antibodies that bind to specific receptors on immune cells like mast cells or basophils. When the allergen appears again it cross-links with these IgE molecules causing degranulation which releases histamine and other mediators into surrounding tissue.
How common are allergies among identical twins compared to non-identical twins?
Identical twins share the same allergic diseases about 70% of the time while non-identical twins show this trait only 40% of the time. Heredity remains the most significant host factor influencing allergy susceptibility across generations.
When was the RAST methodology invented and who developed it?
The RAST methodology was invented and marketed in 1974 by Pharmacia Diagnostics AB in Uppsala Sweden. In 1989 this company replaced it with a superior test named ImmunoCAP Specific IgE blood test using fluorescence-labeled technology.
What percentage of the population develops a strong immune response to urushiol found in poison ivy plants?
Approximately 25% of the population develops a strong immune response to urushiol found in poison ivy plants. This reaction can cause skin contact issues resulting in dry crusted lesions lasting 48 to 96 hours.