Allergies Symptoms and Causes

Other Names: Hipersensitivite, hypersensitivity

What are they?

Allergies are states of hypersensitivity. They are extreme reactions of the immune system of some people to substances that do not cause a reaction in most people. Hypersensitivities are grouped into types ranging from I to IV. These classifications depend to some extent on which parts of the immune system are activated, and how long it takes for the reaction to occur.

Two types of hypersensitivity are often associated with the term “allergies”. Type I is an immediate hypersensitivity reaction, usually occurring within minutes, where  antigens ( allergens , foreign substances) combine with specific  IgE (immunoglobulin E) antibodies, causing localized and sometimes systemic reactions. Type IV delayed hypersensitivity reactions are characterized by antigens and specific sensitized T lymphocytes rather than antibodies .reactions caused by interactions. Although anyone can develop allergies, affected family members are at an increased risk. However, the “prone” person may not react to the same substances as their parents and siblings. The type of reactions depend on the type of antigens they are exposed to and the response of their immune system.

Type I hypersensitivity reaction primarily adversely affects the respiratory and gastrointestinal systems and the skin. The first time the prone person is exposed to a potential antigen, they will not show a significant reaction, will begin to produce a specific IgE antibody and will become “sensitized”. Once a person is sensitized, successive exposures can lead to severe reactions.

The formed IgE antibody attaches itself to specialized mast cells in tissues and basophils in the bloodstream . This action “trains” the immune system. During subsequent exposures to the allergen, specifically bound IgE recognizes the “aggressor”, binds to it, triggers the release of chemicals such as histamine, causing allergic symptoms to appear where the allergen enters, for example in the mouth, nose or skin.

Type IV hypersensitivity reactions usually involve the skin and are referred to as “delayed” hypersensitivity reactions, as they typically occur approximately 48-72 hours after exposure. These reactions occur when an antigen reacts with specifically sensitized T lymphocytes. Lymphocytes release inflammatory and toxic substances and cause tissue damage by attracting other white blood cell (WBC-leukocyte) types to the exposure area. The immune system does not need to be “trained” beforehand. People can have a type IV reaction on the first exposure. An allergy to poison ivy is a typical example of this type of allergy.

What is an allergy?
Although they can cause allergy-like symptoms, there are other reactions that are not triggered by the activation of the immune system. These reactions are toxic reactions that occur as a result of sufficient exposure to bacterial toxins that cause food poisoning, food intolerances due to the deficiency of an enzyme (e.g. milk sugar digestive disorder leading to lactose intolerance, celiac disease ).as well as inherited diseases such as sensitivity to gluten-like substances). Drugs such as aspirin, ampicillin, food dyes, monosodium glutamate, which is a food flavor additive, and some psychological triggers can also cause reactions. Although these diseases and abnormal conditions may need to be investigated by the doctor, they are not allergic reactions and will not be identified during allergy tests.


An acute , type I allergic reaction on the skin causes hives, dermatitis , and itching. When it becomes chronic , it can cause allergic atopic dermatitis and eczema . An acute allergic reaction in the respiratory system causes coughing, nasal congestion, sneezing, a feeling of tightness in the throat and, if chronic, asthma . Acute allergic reactions in the gastrointestinal tract begin with tingling in the mouth, itching, metallic taste, swelling of the tongue and throat, followed by abdominal pain, muscle spasms, vomiting and diarrhea. When it becomes chronic, it causes various gastrointestinal problems.

Any acute allergic reaction has the potential to be life-threatening and leads to anaphylaxis . Anaphylaxis is a multi-organ reaction that may begin with restlessness, a feeling of “approaching doomsday”, pale skin due to low blood pressure, and/or loss of consciousness (fainting). Anaphylaxis can be fatal if adrenaline is not injected quickly. Type I allergic reactions can occur in varying degrees of severity, sometimes causing hay fever, at other times anaphylaxis.

Type I allergies, foods, plants (pollens, grasses, grasses, etc.), pesticides, animal hair and saliva (e.g. cat and dog), dust mites, mold spores , occupational exposures (such as latex) and drugs (eg penicillin) may be in the form of a reaction to various substances, but not limited to. Cross-reactions can also occur, where, for example, someone allergic to ragweed may react to melon or watermelon or banana. Of the foods that most commonly cause an anaphylactic reaction, peanuts, tree nuts such as walnuts, and shellfish include.

Type IV delayed hypersensitivity reactions are most frequently skin reactions. Reaction to nickel is a common example in the metal jewelery business. A type IV hypersensitivity reaction can cause skin redness, swelling, induration, rash, and skin inflammation hours or days after exposure.


The process of diagnosing type I hypersensitivity reactions begins with a careful review of a person’s personal history, such as signs of illness, family history, age at which the reactions begin, seasonal signs, those that occur after exposure to animals, hay, or dust, and those that develop in specific settings, such as the workplace. Environmental pollution, smoking, exercise, alcohol, drugs and stress are factors to consider as they can worsen the symptoms of the disease. After narrowing the list of possible allergens, specific tests can be done.

Laboratory tests:

  • Allergen-specific IgE test: Immunoanalysis and RAST (radioallergen absorption test) : These are the tests used to screen for Type I allergen-specific IgE antibodies. Allergen-specific IgE antibody testing involves taking a blood sample and checking for any suspected allergen . Allergens can be selected individually at a time, or from food panels containing the most frequently detected adult or child food allergens, and panels containing the most common regional grasses and grasses that are airborne in the person’s residence. Individual selections are very specific (like wasp or honeybee, egg white or yolk). The doctor will select the most suitable allergens. Usually, a person will actually be allergic to only a few (4 or fewer) substances.
  • If a specific IgE test is negative, there is a possibility that the person being tested is not allergic to that substance. The test should be evaluated in the context of the person’s clinical history. Although a person may have a low allergen level, they may still have a severe reaction when actually exposed to the allergen, or they may never have a reaction even though the level is high. Children who survive a food allergy may continue to have positive IgE test results for years.
  • Total IgE test : Sometimes done to look for an ongoing allergic process. Although it is a blood test that detects the presence of IgE protein (including allergy antibodies), it does not identify specific allergens. Diseases other than allergies can also cause levels to rise.

Other tests:

  • Skin puncture or scratch test: Often used to detect airborne allergens such as pollen, dust and molds. Skin puncture tests are not usually performed for food allergies because of the potential for severe reactions. The person being tested should not have significant eczema and should not take antihistamines or certain antidepressants for a few days before the skin prick test . If the dosage of the allergen is high enough, false positives can occur even in the non-allergic person.
  • Intradermal allergy skin tests: are based on subcutaneous blister formation by injection of the allergen, but are not widely accepted due to the high false-positive rate .
  • Patch test:   It is the easiest skin and patch (strip) tests used to test for Type IV delayed hypersensitivity. A certain concentration of the suspected allergen is applied to the skin, covered with non-absorbent adhesive tape, and left for 48 hours. If the burning and itching sensation develops faster, the patch is removed. A positive test includes redness, some skin hardening and swelling, and sometimes the formation of blisters ( vesicles) . Since some reactions will not occur until the bands are removed, the test areas are also checked at 72 and 96 hours.
  • Oral food challenge test: They are considered to be the “gold standard” for diagnosing food allergies. They are intensive tests and require strict medical supervision as severe reactions can occur, including life-threatening anaphylaxis . Nutrient challenge tests involve administering small amounts of unlabeled potential food allergens, either in a capsule or intravenously, and observing allergic reactions. Negative results are confirmed by giving more abundant meals in the form of nutrients.
  • Elimination : Another method of testing for food allergies. It involves eliminating all suspected foods from the diet and then incorporating one food at a time to identify the cause(s) of the problem.

Other tests that are not widely recognized as useful:

  • Immunoglobulin G4 (IgG4) antibody
  • Provocation-neutralization
  • cytotoxic test
  • Applied kinesiology
  • Sublingual provocation
  • Neutralization test
  • Nutrient immune complex analysis
  • Dark field video analysis in peripheral blood
  • Infrared analysis

Treatment Prevention

 There is some evidence that breastfed children have fewer types I and IV hypersensitivity reactions. In addition, it is thought that a very limited and “hygienic” environment may play a role in the increase of allergies. Some studies have shown that babies raised on farms are less allergic than those who live in a more allergen-deprived environment.

Avoidance and Elimination:  The best way to prevent a reaction after an allergy has developed is to avoid exposure whenever possible. This approach means eliminating this substance from the diet for life, being on the lookout for hidden ingredients in processed and restaurant foods. For example, a spatula used for peanut candies before serving chocolate chip cookies can trigger a reaction in people sensitive to peanuts.

It is best to avoid insects and animals. If airborne pollen, such as local grasses and grasses, is present, limiting time outside can be helpful but may not prevent the problem from occurring. Some try to move to another area to avoid certain local allergens. This approach may not be effective, as those with allergies often develop new allergies to pollen and grasses in the area they move to.

Desensitization (immunotherapy, specific immunization therapy, “allergy shots”): Sometimes the recommended treatment when the allergen cannot be avoided. Injections of the allergen, given at regular intervals, in increasing doses, “accustom” the body to the allergen. Needles reduce the amount of IgE antibodies in the blood and cause it to form another protective antibody (immunoglobulin G, IgG ). Since it crosses the placental barrier , IgG is important in creating immunity in the baby before birth . Immunotherapy injections can cause side effects such as hives and skin rashes, as well as cause anaphylaxis .can also trigger. Desensitization is most effective in people with hay fever symptoms and severe insect bite allergies. Most people with hay fever can see significant reductions in symptoms within 12 months, and it is effective in about two-thirds of those who try it. People may consider continuing the injections for 3 years and then stopping. In some, it will provide long-term relief, while in others, the symptoms of the disease may reappear. Immunotherapy is not recommended for food allergies.

Short-term symptomatic treatment: It   is used to relieve the symptoms of the disease. For example, if respiratory symptoms are present, treatment may include antihistamines , topical nasal steroids, oral steroids, or decongestants.

In the case of anaphylaxis, adrenaline injections are needed. Those with severe reactions should always carry with them a kit containing an emergency injection of adrenaline. Anyone who reacts and uses adrenaline should seek medical treatment as follow-up treatment is often required.

Sources of the article

Resources Used in This Review

Cost, KD & Cost, TJ (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., St. Louis, MO. Pp 38-44.

(© 2009). Tips to Remember: Allergic Reactions. American Academy of Allergy Asthma and Immunology [On-line information]. through . Internet access date: February 2010.

(© 2009). Tips to Remember: Asthma & Allergy Medications. American Academy of Allergy Asthma and Immunology [On-line bilgiler]. through  İnternete giriş tarihi: Şubat 2010.

Mayo Clinic Staff (June 24, 2009). Allergy medications: Know your options. [On-line information]. . Internet access date: February 2010.

Hinshaw, WD et. get. (Updated June 2, 2009). Hypersensitivity Reactions, Delayed. eMedicine [On-line information]. through . Internet access date: February 2010.

Anand, M. and Routes, J. (Updated June 16, 2009). Hypersensitivity Reactions, Immediate. eMedicine [On-line information]. Internet access date: February 2010.

Mayo Clinic Staff (April 3, 2009). Allergy Skin Tests. [On-line information]. . Internet access date: February 2010.

(© 2009). Tips to Remember: What is Allergy Testing? American Academy of Allergy Asthma and Immunology [On-line information]. . Internet access date: February 2010.

Sources used in previous compilations

Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition]. Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., St. Louis, MO.

Sicherer, S. (15 Ocak 1999). Manifestations of Food Allergy: Evaluation and Management. American Family Physician [On-line serial].

American Academy of Family Physicians (15 Ocak 1999). Food Allergies—Just the Facts. American Family Physician [On-line serisi].

ARUP. Immunoglobulin E. Guide to Clinical Laboratory Testing [On-line bilgiler].

Sicherer, S. (Last revised April 5, 2001). Food Allergy Testing: Questions and Answers. Food Allergy News Reprint [On-line information]. .

Formanek, R. (Temmuz-Ağustos 2001). Food Allergies: When Food Becomes the Enemy. U.S. Food and Drug Administration, FDA Consumer magazine [On-line serisi].

MEDLINEplus (Updated January 2, 2002). Allergies. MEDLINEplus Health Information [On-line information]. .

MEDLINEplus (Updated January 2, 2002 ). Allergy testing. MEDLINEplus Health Information [On-line information]. .

WAO [2000-2002]. Overview of Allergy, Its Diagnosis and Treatment. World Allergy Organization [On-line bilgiler].

National Institute of Allergy and Infectious Disease (Şubat 1998 ). Something in the Air: Airborne Allergens. WebMD [On-line dizi]. through

National Institute of Allergy and Infectious Diseases (1999 January, last revision). Food Allergy and Intolerances. WebMD [On-line dizi].

Mellors, R. C., (1999, July 30). Immunopathology, Hypersensitivity Reactions. Weill Medical College of Cornell University [On-line makale ].

Allergy glossary. Type IV (delayed or cell-mediated) Hypersensitivity. Health on the Net Foundation [On-line bilgiler].

Allergy glossary. Antibody (Ab), Immunoglobulin, Immunoglobulin E (IgE), and Immunoglobulin G (IgG). Health on the Net Foundation [On-line bilgiler].

Merck. Hypersensitivity Disorders, General. The Merck Manual of Diagnosis and Therapy [On-line yayın].

Merck. Disorders With Type I Hypersensitivity Reactions. The Merck Manual of Diagnosis and Therapy [On-line yayın].

Merck. Disorders With Type IV Hypersensitivity Reactions. The Merck Manual of Diagnosis and Therapy [On-line yayın].

Martz, Eric, page maintenance (31 Mart 1997). Poison Ivy: an Exaggerated Immune Response to Nothing Much [On-line makale].

Haskell, J., Webbed by (Son Güncelleştirme tarihi: 15 Mart 1996)  Practice Parameters for Allergy Diagnostic Testing. Reprint from: Annals of Allergy, Asthma, & Immunology [Journal], vol 75(6).

Leave a Comment