What happens when you have an allergy biology
After the chemical mediators of the acute response subside, late-phase responses can often happen. This is due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils and macrophages to the initial site.
The reaction is generally seen 2–24 hours after the original reaction. Cytokines from mast cells may frolic a role in the persistence of long-term effects. Late-phase responses seen in asthma are slightly diverse from those seen in other allergic responses, although they are still caused by release of mediators from eosinophils and are still dependent on activity of TH2 cells.
In the early stages of allergy, a type I hypersensitivity reaction against an allergen encountered for the first time and presented by a professional antigen-presenting cell causes a response in a type of immune cell called a TH2 lymphocyte; a subset of T cells that produce a cytokine called interleukin-4 (IL-4).
These TH2 cells interact with other lymphocytes called B cells, whose role is production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to start production of a large quantity of a specific type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a helpful of Fc receptor called FcεRI) on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage, are sensitized to the allergen.
If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils.
Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complicated interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth muscle contraction.
This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis. Depending on the individual, allergen, and mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to specific body systems; asthma is localized to the respiratory system and eczema is localized to the dermis.
Allergic contact dermatitis
Although allergic contact dermatitis is termed an «allergic» reaction (which generally refers to type I hypersensitivity), its pathophysiology actually involves a reaction that more correctly corresponds to a type IV hypersensitivity reaction. In type IV hypersensitivity, there is activation of certain types of T cells (CD8+) that destroy target cells on contact, as well as activated macrophages that produce hydrolyticenzymes.
Effective management of allergic diseases relies on the ability to make an precise diagnosis. Allergy testing can assist confirm or law out allergies. Correct diagnosis, counseling, and avoidance advice based on valid allergy test results reduces the incidence of symptoms and need for medications, and improves quality of life. To assess the presence of allergen-specific IgE antibodies, two diverse methods can be used: a skin prick test, or an allergy blood test.
Both methods are recommended, and they own similar diagnostic value.
Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test. Also, early and more precise diagnoses save cost due to reduced consultations, referrals to secondary care, misdiagnosis, and emergency admissions.
Allergy undergoes dynamic changes over time.
Regular allergy testing of relevant allergens provides information on if and how patient management can be changed, in order to improve health and quality of life.
Annual testing is often the practice for determining whether allergy to milk, egg, soy, and wheat own been outgrown, and the testing interval is extended to 2–3 years for allergy to peanut, tree nuts, fish, and crustacean shellfish. Results of follow-up testing can guide decision-making regarding whether and when it is safe to introduce or re-introduce allergenic food into the diet.
Challenge testing: Challenge testing is when little amounts of a suspected allergen are introduced to the body orally, through inhalation, or via other routes.
Except for testing food and medication allergies, challenges are rarely performed. When this type of testing is chosen, it must be closely supervised by an allergist.
Elimination/challenge tests: This testing method is used most often with foods or medicines. A patient with a suspected allergen is instructed to modify his diet to totally avoid that allergen for a set time. If the patient experiences significant improvement, he may then be «challenged» by reintroducing the allergen, to see if symptoms are reproduced.
Unreliable tests: There are other types of allergy testing methods that are unreliable, including applied kinesiology (allergy testing through muscle relaxation), cytotoxicity testing, urine autoinjection, skin titration (Rinkel method), and provocative and neutralization (subcutaneous) testing or sublingual provocation.
Skin prick testing
Skin testing is also known as «puncture testing» and «prick testing» due to the series of tiny punctures or pricks made into the patient’s skin.
Little amounts of suspected allergens and/or their extracts (e.g., pollen, grass, mite proteins, peanut extract) are introduced to sites on the skin marked with pen or dye (the ink/dye should be carefully selected, lest it cause an allergic response itself). A little plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected «intradermally» into the patient’s skin, with a needle and syringe.
Common areas for testing include the inside forearm and the back.
If the patient is allergic to the substance, then a visible inflammatory reaction will generally happen within 30minutes. This response will range from slight reddening of the skin to a full-blown hive (called «wheal and flare») in more sensitive patients similar to a mosquito bite. Interpretation of the results of the skin prick test is normally done by allergists on a scale of severity, with +/− meaning borderline reactivity, and 4+ being a large reaction.
Increasingly, allergists are measuring and recording the diameter of the wheal and flare reaction. Interpretation by well-trained allergists is often guided by relevant literature. Some patients may believe they own sure their own allergic sensitivity from observation, but a skin test has been shown to be much better than patient observation to detect allergy.
If a serious life-threatening anaphylactic reaction has brought a patient in for evaluation, some allergists will prefer an initial blood test prior to performing the skin prick test. Skin tests may not be an option if the patient has widespread skin disease, or has taken antihistamines in the final several days.
Main article: Patch test
Patch testing is a method used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed reactions. It is used to assist ascertain the cause of skin contact allergy, or contact dermatitis.
Adhesive patches, generally treated with a number of common allergic chemicals or skin sensitizers, are applied to the back. The skin is then examined for possible local reactions at least twice, generally at 48 hours after application of the patch, and again two or three days later.
An allergy blood test is quick and simple, and can be ordered by a licensed health care provider (e.g., an allergy specialist) or general practitioner. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can get an allergy blood test.
For babies and extremely young children, a single needle stick for allergy blood testing is often more tender than several skin pricks.
An allergy blood test is available through most laboratories. A sample of the patient’s blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are extremely safe, since the person is not exposed to any allergens during the testing procedure.
The test measures the concentration of specific IgE antibodies in the blood. Quantitative IgE test results increase the possibility of ranking how diverse substances may affect symptoms.
A law of thumb is that the higher the IgE antibody worth, the greater the likelihood of symptoms. Allergens found at low levels that today do not result in symptoms can not assist predict future symptom development. The quantitative allergy blood result can assist determine what a patient is allergic to, assist predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity.
A low entire IgE level is not adequate to law out sensitization to commonly inhaled allergens.Statistical methods, such as ROC curves, predictive worth calculations, and likelihood ratios own been used to examine the relationship of various testing methods to each other.
These methods own shown that patients with a high entire IgE own a high probability of allergic sensitization, but further investigation with allergy tests for specific IgE antibodies for a carefully chosen of allergens is often warranted.
Laboratory methods to measure specific IgE antibodies for allergy testing include enzyme-linked immunosorbent assay (ELISA, or EIA),radioallergosorbent test (RAST) and fluorescent enzyme immunoassay (FEIA).
Before a diagnosis of allergic disease can be confirmed, other possible causes of the presenting symptoms should be considered.Vasomotor rhinitis, for example, is one of numerous illnesses that share symptoms with allergic rhinitis, underscoring the need for professional differential diagnosis. Once a diagnosis of asthma, rhinitis, anaphylaxis, or other allergic disease has been made, there are several methods for discovering the causative agent of that allergy.
Risk factors for allergy can be placed in two general categories, namely host and environmental factors. Host factors include heredity, sex, race, and age, with heredity being by far the most significant. However, there own been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in exposure to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.
Main article: Hygiene hypothesis
Allergic diseases are caused by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response.
Numerous bacteria and viruses elicit a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis was that insufficient stimulation of the TH1 arm of the immune system leads to an overactive TH2 arm, which in turn leads to allergic disease. In other words, individuals living in too sterile an environment are not exposed to enough pathogens to hold the immune system busy. Since our bodies evolved to deal with a certain level of such pathogens, when they are not exposed to this level, the immune system will attack harmless antigens and thus normally benign microbial objects—like pollen—will trigger an immune response.
The hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were, it is presumed, exposed to more infectious agents through their siblings, than in children from families with only one kid.
The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become an significant theoretical framework for the study of allergic disorders. It is used to explain the increase in allergic diseases that own been seen since industrialization, and the higher incidence of allergic diseases in more developed countries. The hygiene hypothesis has now expanded to include exposure to symbiotic bacteria and parasites as significant modulators of immune system development, along with infectious agents.
Epidemiological data support the hygiene hypothesis. Studies own shown that various immunological and autoimmune diseases are much less common in the developing world than the industrialized world and that immigrants to the industrialized world from the developing world increasingly develop immunological disorders in relation to the length of time since arrival in the industrialized world. Longitudinal studies in the third world protest an increase in immunological disorders as a country grows more affluent and, it is presumed, cleaner. The use of antibiotics in the first year of life has been linked to asthma and other allergic diseases. The use of antibacterial cleaning products has also been associated with higher incidence of asthma, as has birth by Caesarean section rather than vaginal birth.
Latex can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction.
The prevalence of latex allergy in the general population is believed to be less than one percent. In a hospital study, 1 in surgical patients ( percent) reported latex sensitivity, although the sensitivity among healthcare workers is higher, between seven and ten percent. Researchers attribute this higher level to the exposure of healthcare workers to areas with significant airborne latex allergens, such as operating rooms, intensive-care units, and dental suites. These latex-rich environments may sensitize healthcare workers who regularly inhale allergenic proteins.
The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions.
This reaction generally lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations.Anaphylactic reactions happen most often in sensitive patients who own been exposed to a surgeon’s latex gloves during abdominal surgery, but other mucosal exposures, such as dental procedures, can also produce systemic reactions.
Latex and banana sensitivity may cross-react.
Furthermore, those with latex allergy may also own sensitivities to avocado, kiwifruit, and chestnut. These people often own perioral itching and local urticaria. Only occasionally own these food-induced allergies induced systemic responses. Researchers suspect that the cross-reactivity of latex with banana, avocado, kiwifruit, and chestnut occurs because latex proteins are structurally homologous with some other plant proteins.
Main article: Food allergy
A wide variety of foods can cause allergic reactions, but 90% of allergic responses to foods are caused by cow’s milk, soy, eggs, wheat, peanuts, tree nuts, fish, and shellfish. Other food allergies, affecting less than 1 person per 10, population, may be considered «rare». The use of hydrolysed milk baby formula versus standard milk baby formula does not appear to change the risk.
The most common food allergy in the US population is a sensitivity to crustacea. Although peanut allergies are notorious for their severity, peanut allergies are not the most common food allergy in adults or children.
Severe or life-threatening reactions may be triggered by other allergens, and are more common when combined with asthma.
Rates of allergies differ between adults and children. Peanut allergies can sometimes be outgrown by children. Egg allergies affect one to two percent of children but are outgrown by about two-thirds of children by the age of 5. The sensitivity is generally to proteins in the white, rather than the yolk.
Milk-protein allergies are most common in children. Approximately 60% of milk-protein reactions are immunoglobulin E-mediated, with the remaining generally attributable to inflammation of the colon. Some people are unable to tolerate milk from goats or sheep as well as from cows, and numerous are also unable to tolerate dairy products such as cheese.
Roughly 10% of children with a milk allergy will own a reaction to beef. Beef contains little amounts of proteins that are present in greater abundance in cow’s milk.Lactose intolerance, a common reaction to milk, is not a form of allergy at every, but rather due to the absence of an enzyme in the digestive tract.
Those with tree nut allergies may be allergic to one or to numerous tree nuts, including pecans, pistachios, pine nuts, and walnuts. Also seeds, including sesame seeds and poppy seeds, contain oils in which protein is present, which may elicit an allergic reaction.
Allergens can be transferred from one food to another through genetic engineering; however genetic modification can also remove allergens. Little research has been done on the natural variation of allergen concentrations in unmodified crops.
Main article: Insect sting allergy
Typically, insects which generate allergic responses are either stinging insects (wasps, bees, hornets and ants) or biting insects (mosquitoes, ticks).
Stinging insects inject venom into their victims, whilst biting insects normally introduce anti-coagulants.
Allergic diseases are strongly familial: identical twins are likely to own the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins. Allergic parents are more likely to own allergic children, and those children’s allergies are likely to be more severe than those in children of non-allergic parents.
Some allergies, however, are not consistent along genealogies; parents who are allergic to peanuts may own children who are allergic to ragweed. It seems that the likelihood of developing allergies is inherited and related to an irregularity in the immune system, but the specific allergen is not.
The risk of allergic sensitization and the development of allergies varies with age, with young children most at risk. Several studies own shown that IgE levels are highest in childhood and drop rapidly between the ages of 10 and 30 years. The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 
Overall, boys own a higher risk of developing allergies than girls, although for some diseases, namely asthma in young adults, females are more likely to be affected. These differences between the sexes tend to decrease in adulthood.
Ethnicity may frolic a role in some allergies; however, racial factors own been hard to separate from environmental influences and changes due to migration. It has been suggested that diverse genetic loci are responsible for asthma, to be specific, in people of European, Hispanic, Asian, and African origins.
Chronic stress can aggravate allergic conditions.
This has been attributed to a T helper 2 (TH2)-predominant response driven by suppression of interleukin 12 by both the autonomic nervous system and the hypothalamic–pituitary–adrenal axis. Stress management in highly susceptible individuals may improve symptoms.
Toxins interacting with proteins
Another non-food protein reaction, urushiol-induced contact dermatitis, originates after contact with poison ivy, eastern poison oak, western poison oak, or poison sumac. Urushiol, which is not itself a protein, acts as a hapten and chemically reacts with, binds to, and changes the shape of integral membrane proteins on exposed skin cells.
The immune system does not recognize the affected cells as normal parts of the body, causing a T-cell-mediated immune response. Of these poisonous plants, sumac is the most virulent. The resulting dermatological response to the reaction between urushiol and membrane proteins includes redness, swelling, papules, vesicles, blisters, and streaking.
Estimates vary on the percentage of the population that will own an immune system response. Approximately 25 percent of the population will own a strong allergic response to urushiol. In general, approximately 80 percent to 90 percent of adults will develop a rash if they are exposed to milligrams (×10−5gr) of purified urushiol, but some people are so sensitive that it takes only a molecular trace on the skin to initiate an allergic reaction.
Main article: Drug allergy
See also: Adverse drug reaction and Drug eruption
About 10% of people report that they are allergic to penicillin; however, 90% turn out not to be. Serious allergies only happen in about %.
Other environmental factors
There are differences between countries in the number of individuals within a population having allergies.
Allergic diseases are more common in industrialized countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in urban populations versus rural populations, although these differences are becoming less defined. Historically, the trees planted in urban areas were predominantly male to prevent litter from seeds and fruits, but the high ratio of male trees causes high pollen counts.
Alterations in exposure to microorganisms is another plausible explanation, at present, for the increase in atopic allergy. Endotoxin exposure reduces release of inflammatory cytokines such as TNF-α, IFNγ, interleukin, and interleukin from white blood cells (leukocytes) that circulate in the blood. Certain microbe-sensing proteins, known as Toll-like receptors, found on the surface of cells in the body are also thought to be involved in these processes.
Gutworms and similar parasites are present in untreated drinking water in developing countries, and were present in the water of developed countries until the routine chlorination and purification of drinking water supplies. Recent research has shown that some common parasites, such as intestinal worms (e.g., hookworms), secrete chemicals into the gut wall (and, hence, the bloodstream) that suppress the immune system and prevent the body from attacking the parasite. This gives rise to a new slant on the hygiene hypothesis theory—that co-evolution of humans and parasites has led to an immune system that functions correctly only in the presence of the parasites.
Without them, the immune system becomes unbalanced and oversensitive. In specific, research suggests that allergies may coincide with the delayed establishment of gut flora in infants. However, the research to support this theory is conflicting, with some studies performed in China and Ethiopia showing an increase in allergy in people infected with intestinal worms. Clinical trials own been initiated to test the effectiveness of certain worms in treating some allergies. It may be that the term ‘parasite’ could turn out to be inappropriate, and in fact a hitherto unsuspected symbiosis is at work. For more information on this topic, see Helminthic therapy.
Further information: Allergy prevention in children
Giving peanut products early may decrease the risk allergies while only breastfeeding during at least the first few months of life may decrease the risk of dermatitis. There is no excellent evidence that a mother’s diet during pregnancy or breastfeeding affects the risk. Nor is there evidence that delayed introduction of certain foods is useful. Early exposure to potential allergens may actually be protective.
Fish oil supplementation during pregnancy is associated with a lower risk. Probiotic supplements during pregnancy or infancy may assist to prevent atopic dermatitis.
Management of allergies typically involves avoiding what triggers the allergy and medications to improve the symptoms.Allergen immunotherapy may be useful for some types of allergies.
Main article: Allergen immunotherapy
Allergen immunotherapy is useful for environmental allergies, allergies to insect bites, and asthma. Its benefit for food allergies is unclear and thus not recommended. Immunotherapy involves exposing people to larger and larger amounts of allergen in an effort to change the immune system’s response.
Meta-analyses own found that injections of allergens under the skin is effective in the treatment in allergic rhinitis in children and in asthma. The benefits may final for years after treatment is stopped. It is generally safe and effective for allergic rhinitis and conjunctivitis, allergic forms of asthma, and stinging insects.
The evidence also supports the use of sublingual immunotherapy for rhinitis and asthma but it is less strong. For seasonal allergies the benefit is small. In this form the allergen is given under the tongue and people often prefer it to injections. Immunotherapy is not recommended as a stand-alone treatment for asthma.
Several medications may be used to block the action of allergic mediators, or to prevent activation of cells and degranulation processes.
These include antihistamines, glucocorticoids, epinephrine (adrenaline), mast cell stabilizers, and antileukotriene agents are common treatments of allergic diseases.Anti-cholinergics, decongestants, and other compounds thought to impair eosinophilchemotaxis, are also commonly used.
Although rare, the severity of anaphylaxis often requires epinephrine injection, and where medical care is unavailable, a device known as an epinephrine autoinjector may be used.
An experimental treatment, enzyme potentiated desensitization (EPD), has been tried for decades but is not generally accepted as effective. EPD uses dilutions of allergen and an enzyme, beta-glucuronidase, to which T-regulatory lymphocytes are supposed to reply by favoring desensitization, or down-regulation, rather than sensitization.
EPD has also been tried for the treatment of autoimmune diseases but evidence does not show effectiveness.
A review found no effectiveness of homeopathic treatments and no difference compared with placebo. The authors concluded that, based on rigorous clinical trials of every types of homeopathy for childhood and adolescence ailments, there is no convincing evidence that supports the use of homeopathic treatments.
According to the National Middle for Complementary and Integrative Health, U.S, the evidence is relatively strong that saline nasal irrigation and butterbur are effective, when compared to other alternative medicine treatments, for which the scientific evidence is feeble, negative, or nonexistent, such as honey, acupuncture, omega 3’s, probiotics, astragalus, capsaicin, grape seed extract, Pycnogenol, quercetin, spirulina, stinging nettle, tinospora or guduchi.
The allergic diseases—hay fever and asthma—have increased in the Western world over the past 2–3 decades. Increases in allergic asthma and other atopic disorders in industrialized nations, it is estimated, began in the s and s, with further increases occurring during the s and s, although some propose that a steady rise in sensitization has been occurring since the s. The number of new cases per year of atopy in developing countries has, in general, remained much lower.
|Allergytype||United States||United Kingdom|
|Allergicrhinitis||million (about 11% of the population)||million (about % of the population)|
|Asthma||10 million own allergic asthma (about 3% of the population).
The prevalence of asthma increased 75% from to Asthma prevalence is 39% higher in African Americans than in Europeans.
|million (about %). In six- and seven-year-olds asthma increased from % to % over five years, during the same time the rate decreased from 31% to % in to year-olds.|
|Atopic eczema||About 9% of the population. Between and , prevalence has increased from 3% to 10% in children.||million (about 1% severe).|
|Anaphylaxis||At least 40 deaths per year due to insect venom. About deaths due to penicillin anaphylaxis. About cases of anaphylaxis and 3 deaths per year are due to latex allergy. An estimated people die annually from anaphylaxis due to food allergy.||Between and , 48 deaths occurred in people ranging from five months to 85 years ancient.|
|Insect venom||Around 15% of adults own mild, localized allergic reactions. Systemic reactions happen in 3% of adults and less than 1% of children.||Unknown|
|Drug allergies||Anaphylactic reactions to penicillin cause deaths per year.||Unknown|
|Food allergies||About 6% of US children under age 3 and –4% of the overall US population. Peanut and/or tree nut (e.g.
A summary diagram that explains how allergy developsDegranulation process in allergy. Second exposure to allergen. 1 – antigen; 2 – IgE antibody; 3 – FcεRI receptor; 4 – preformed mediators (histamine, proteases, chemokines, heparin); 5 – granules; 6 – mast cell; 7 – newly formed mediators (prostaglandins, leukotrienes, thromboxanes, PAF).An allergy testing machine being operated in a diagnostic immunology labAnti-allergy immunotherapy
Immunology is the study of the immune system and is a extremely significant branch of the medical and biological sciences.
The immune system protects us from infection through various lines of defence. If the immune system is not functioning as it should, it can result in disease, such as autoimmunity, allergy and cancer. It is also now becoming clear that immune responses contribute to the development of numerous common disorders not traditionally viewed as immunologic, including metabolic, cardiovascular, and neurodegenerative conditions such as Alzheimer’s.
Signs and symptoms
|Affected organ||Common signs and symptoms|
|Nose||Swelling of the nasal mucosa (allergic rhinitis) runny nose, sneezing|
|Eyes||Redness and itching of the conjunctiva (allergic conjunctivitis, watery)|
|Airways||Sneezing, coughing, bronchoconstriction, wheezing and dyspnea, sometimes outright attacks of asthma, in severe cases the airway constricts due to swelling known as laryngeal edema|
|Ears||Feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.|
|Skin||Rashes, such as eczema and hives (urticaria)|
|Gastrointestinal tract||Abdominal pain, bloating, vomiting, diarrhea|
Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance, allergic rhinitis, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes. Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing.
Aside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications love aspirin and antibiotics such as penicillin.
Symptoms of food allergy include abdominal pain, bloating, vomiting, diarrhea, itchy skin, and swelling of the skin during hives. Food allergies rarely cause respiratory (asthmatic) reactions, or rhinitis. Insect stings, food, antibiotics, and certain medicines may produce a systemic allergic response that is also called anaphylaxis; multiple organ systems can be affected, including the digestive system, the respiratory system, and the circulatory system. Depending on the rate of severity, anaphylaxis can include skin reactions, bronchoconstriction, swelling, low blood pressure, coma, and death.
This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a period of time.
Substances that come into contact with the skin, such as latex, are also common causes of allergic reactions, known as contact dermatitis or eczema. Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a «weal and flare» reaction characteristic of hives and angioedema.
With insect stings a large local reaction may happen (an area of skin redness greater than 10cm in size). It can final one to two days. This reaction may also happen after immunotherapy.