What is Type I Hypersensitivity Reaction?

The immune system is like a defense force for our body, keeping us healthy and safe from harmful germs. But sometimes, it can overreact, leading to an exaggerated defensive response that can cause negative health effects. These overreactions are known as hypersensitivity reactions.

There are four main categories of hypersensitivity reactions: Type I, Type II, Type III, and Type IV.

In Type I hypersensitivity, also called an immediate reaction, the immune system creates IgE antibodies that trigger the release of histamine and other chemicals causing inflammation. This reaction can result in conditions such diseases related to allergies such as asthma, hay fever, and certain skin, eye, and food allergies.

Type II hypersensitivity, or cytotoxic reactions, happen when antibodies damage or destroy cells. Type III hypersensitivity also known as immune complex reactions, involves not only IgG and IgM but sometimes IgA antibodies as well. The immune system forms complexes that can cause damage to tissues. Lastly, Type IV hypersensitivity is a delayed reaction, and it’s caused by T-cell reactions, which can also lead to tissue damage.

Recently, some researchers added three more classifications to these traditional four ones. However, in this instance, we’re primarily focusing on Type I hypersensitivity reactions.

Type I hypersensitivities can be triggered by substances that are harmless for most people, like pollen or certain foods, or by harmful substances like insect venoms. How the reaction shows up depends on where in the body it occurs. It can cause hay fever (nose), allergic conjunctivitis (eyes), hives or eczema (skin), angioedema (soft tissue), allergic asthma (lungs), or even anaphylaxis, a serious systemic reaction that can be life-threatening.

Some things can increase the risk of allergic diseases, like where you live, environmental issues like pollution, how financially well-off your community is, your genes, and a surprising theory known as the “hygiene hypothesis”. This hypothesis suggests that the cleaner our modern society is, the less we’re exposed to different microbes and particles from a younger age, which potentially could lead to higher rates of allergies, asthma, and other immune disorders. This theory suggests that exposure to a variety of microbes from an early age might actually decrease these risks.

What Causes Type I Hypersensitivity Reaction?

Type I hypersensitivity is a reaction that our body has when it encounters something it sees as harmful, also known as an antigen. This reaction happens in two stages: sensitization and effect.

In the sensitization stage, our body quietly comes into contact with the antigen without showing any symptoms. In the effect stage, our body encounters the antigen for a second time. This time, it treats the antigen as a threat, triggering an allergic or immune response.

There are many types of antigens that our body can react to. These include food allergies like nuts, eggs, soy, wheat, and shellfish, as well as sources from animals like bees, wasps, insects, cats, and rats.

Environmental allergies from things like dust mites, pollen, mold, and latex can also trigger this type of reaction. Other things that can cause this reaction are atopic diseases like allergic asthma, allergies of the nose and eyes, skin inflammation, allergic reactions during blood transfusions, allergic reactions to medications like antibiotics, hives, or even a severe allergic reaction known as anaphylaxis.

Risk Factors and Frequency for Type I Hypersensitivity Reaction

Type I hypersensitivity, including severe reactions like anaphylaxis, is somewhat difficult to track because people’s reactions can vary in severity. However, studies suggest that between 1% and 2% of people worldwide might experience anaphylaxis, with this condition being more common in younger individuals.

European research indicates that roughly 0.3% of the population may experience anaphylaxis in their lifetime.
In the United States, it’s estimated that between 1.21% and 15.04% of people might encounter anaphylaxis at some point.
Atopic disorders, which includes things like food allergies, allergic reactions in the nose and eyes, skin rashes, and asthma, are increasing. Currently, they affect up to 20-30% of the population.

Signs and Symptoms of Type I Hypersensitivity Reaction

To diagnose Type I hypersensitivity, also known as an allergic reaction, it’s important to get a full account of the patient’s history. This includes:

The signs and symptoms they have experienced
When these symptoms began
Anything the patient ate, or new substances or foods they encountered which might have caused the reaction
Whether or not they’ve been exposed to the allergen before
Any past instances of allergic reactions
Whether they have a history of atopy (conditions like allergic rhinitis, asthma, eczema) or food allergies
Whether the patient has a fever, as fever is not common in Type I reactions
A review of their medical records and known allergies, especially if the patient cannot communicate properly

Just taking a medical history isn’t enough to diagnose an allergic reaction. A complete physical examination is also necessary. The symptoms a patient shows largely depend on which organs are affected. Usually, a response to this kind of hypersensitivity occurs within an hour of the patient coming into contact with the allergen.

Some common symptoms of this allergic reaction include a rash, hives, redness of the skin, itching, swelling, facial flushing, bronchospasm, wheezing, runny nose, and stomach symptoms like abdominal cramping. A characteristic sign of an IgE mediated reaction are “wheal-and-flare” reactions, which are raised, red skin bumps. Patients having an anaphylactic reaction might also experience blackouts, nausea, vomiting, swollen areas, low blood pressure, tachycardia (rapid heart rate), tachypnea (rapid breathing), and so forth. Evaluating for anaphylaxis involves checking the airways, breathing, circulation, and mental status as first steps.

Testing for Type I Hypersensitivity Reaction

There are two types of tests that can help doctors diagnose Type I hypersensitivity – tests done inside the body while taking samples (in-vivo) and tests done outside the body in a laboratory (in-vitro).

In the lab, doctors can check for different indicators in your blood that might suggest an increased risk of anaphylaxis or severe allergic reaction. For instance, an elevated level of a substance called serum tryptase, which is released by certain cells in our immune system when they’re activated, can suggest a higher chance of anaphylaxis.

They may also look for a higher count of white blood cells called eosinophils, which often increase in allergic conditions. They might check the levels of a particular antibody called IgE – this can sometimes be increased in allergic conditions, but it’s not always a reliable marker.

Doctors can also use tests that are more specific, called allergen-specific IgE tests, to identify specific food or other allergies. Another test they might run checks your blood levels of a substance called histamine, but this test is not always reliable because histamine levels can fluctuate rapidly.

Doctors can also use a test called a Flow cytometric basophil activation test (BAT), which is helpful in diagnosing certain drug allergies. This test identifies markers on cells that are activated by drug allergens.

When it comes to in-vivo tests, these are usually done in an outpatient setting like a doctor’s office. One common test is a skin test, which involves introducing small amounts of a potential allergen into your skin and watching for an allergic reaction. A positive reaction is usually a red, itchy bump on the skin within 15-20 minutes.

While skin tests can be extremely helpful, they’re not without risk – the more invasive the test, the lower the rate of false negatives, but also the higher chance of a severe allergic reaction, or anaphylaxis.

Other in-vivo tests might include things like a drug provocation test (done to confirm a specific drug allergy), spirometry or pulmonary function tests (used to check for asthma), or challenges where you inhale specific allergens or compounds to check for airway hypersensitivity.

Sometimes, doctors may also take samples of your mucus (from a nasal smear or induced sputum) to check for an increased number of eosinophils as well.

Treatment Options for Type I Hypersensitivity Reaction

The way a patient is treated for type I hypersensitivity (an allergic reaction) will depend on the specific symptoms they are experiencing and what caused the reaction.

Anaphylaxis is a severe and potentially life-threatening allergic reaction that requires immediate medical attention. If someone is experiencing anaphylaxis, they should be positioned lying down, with their legs raised, unless this could worsen their breathing difficulties. If anaphylaxis is suspected, an injection of the medicine epinephrine (also known as adrenaline) will be given, which can help reduce the severity of the reaction. In some cases, if a person has a history of severe allergic reactions, they would carry a prescription kit for self-treatment that can include: epinephrine, bronchodilators (medicines that help open up the airways), antihistamines (medicines that work against the chemical histamine which is released during an allergic reaction), and corticosteroids (anti-inflammatory medicines).

After the initial treatment with epinephrine, further treatment to help control symptoms may include:
– Beta-agonists such as albuterol, for treating difficulty in breathing.
– Antihistamines like diphenhydramine or famotidine, which can help alleviate symptoms like itching or hives.
– Finally, glucocorticoids, a type of steroid medicine, may be used to help prevent the reaction from returning.

Urticarial or angioedema are types of skin reactions that produce hives and swelling. The treatment is similar to anaphylaxis, where the cause of the reaction is removed if known, and the patient is given antihistamines and glucocorticoids for symptom relief.

For conditions such as allergic asthma, allergic rhinitis (hay fever), allergic conjunctivitis (eye irritation), allergic dermatitis (skin irritation), eczema, wasp or bee venom allergies, drug allergies or food allergies, the first step in treatment is to try to avoid whatever is causing the allergic reaction. Oral or topical antihistamines and oral or inhaled glucocorticoids may be used to help manage symptoms. For allergic asthma, specific asthma medications like inhaled beta-agonists may also be used.

If someone has allergies that significantly affect their life, and if avoiding the allergen or using medicines to relieve symptoms hasn’t worked, allergen immunotherapy – also known as allergy shots – can be considered. This involves regular injections of gradually increasing amounts of the allergen, with the aim of causing the body’s immune system to become less sensitive to it.

Some diseases can have symptoms similar to type I hypersensitivities, making it difficult to diagnose. These diseases might include:

Lung diseases such as acute non-allergic asthma, chronic obstructive pulmonary disease (COPD), emphysema, or pneumothorax
Swallowing of foreign objects
Epiglottitis (inflammation in your throat)
Hereditary angioedema (swelling in some parts of the body)
Irritable bowel syndrome
Upper respiratory infections
Syncope (fainting)
Panic or anxiety attacks
Generalized urticaria (hives) caused by infection or hot or cold stimuli

Moreover, some types of shocks mimic anaphylaxis, which can complicate diagnosis. These include:

Hypovolemic shock, due to things like a ruptured ectopic pregnancy, or systemic capillary leak syndrome
Cardiogenic shock (heart can’t pump enough blood)
Distributive shock, like from sepsis
Obstructive shock such as from a blood clot in the lungs or cardiac tamponade

Additionally, certain medications and conditions can cause reactions that look like but aren’t anaphylaxis. For instance:

Fast infusion of the antibiotic vancomycin may lead to the ‘red man syndrome’
Alcohol
Neuroendocrine tumours (carcinoid syndrome)
Perimenopause
Nonorganic diseases that need to be differentiated, such as psychosomatic episodes, or Munchausen stridor, or anaphylaxis in which the patient self-induces the reaction by purposely ingesting the offending agent

What to expect with Type I Hypersensitivity Reaction

The future health outcomes for Type 1 hypersensitivity, a type of immune system overreaction to certain triggers, can be greatly influenced by how severe the reaction is. Usually, these reactions don’t last long and as long as you manage symptoms or avoid the trigger, the risk of harm is low.

However, it can occasionally become a life-threatening situation within minutes if signs or symptoms of conditions like angioedema (swelling under the skin), anaphylaxis (a severe allergic reaction), or severe asthma aren’t quickly spotted and treated.

Additionally, the risk of death from these conditions can get higher with age, with adults being about 7 times more at risk than children. It’s also worth noting that black people have approximately a 75% greater risk compared to white people, and females have a 30% higher risk.

Possible Complications When Diagnosed with Type I Hypersensitivity Reaction

As mentioned before, the most dangerous complication of Type I hypersensitivity or severe allergic reaction is anaphylaxis, which can potentially cause a fatality. During an anaphylactic reaction, the person may experience:

Low blood pressure (hypotension)
Difficulty in breathing or lack of oxygen (hypoxia)
Failure of circulation system (distributive shock)

Preventing Type I Hypersensitivity Reaction

Patients should be informed about several key points:

First, they should know how to confirm the cause of anaphylaxis, a severe allergic reaction, and understand their emergency care plan. This plan can be found online and printed in different languages from resources like Food Allergy Research and Education (FARE).

Second, patients must know how to properly treat anaphylaxis. They should be familiar with the correct use of rescue medications, such as inhalers, which are used to help make breathing easier in case of an allergic reaction.

Third, patients should recognize the importance of getting an epinephrine prescription as soon as possible. Epinephrine, also known as adrenaline, is a medicine used to treat severe allergic reactions.

Furthermore, patients need to know the right way to use and store an epinephrine auto-injector, a device for injecting a measured dose or doses of epinephrine by means of autoinjector technology. It is vital to have on hand in case of an allergic reaction.

Avoiding the allergen, or the substance causing the allergic reaction, is very important to prevent future episodes of anaphylaxis.

Lastly, patients should understand the importance of routine follow-up checks with their primary care doctor and an allergist, a doctor who specializes in allergies.

They should also be aware of foods, medications, or other substances that might be related to their allergen and could also potentially trigger a reaction.

Frequently asked questions

Type I hypersensitivity, also known as an immediate reaction, is a type of hypersensitivity reaction where the immune system produces IgE antibodies that trigger the release of histamine and other chemicals, causing inflammation. This can result in conditions such as allergies, asthma, and certain skin, eye, and food allergies.

Between 1% and 2% of people worldwide might experience anaphylaxis, with this condition being more common in younger individuals.

Some signs and symptoms of Type I Hypersensitivity Reaction include: - Rash - Hives - Redness of the skin - Itching - Swelling - Facial flushing - Bronchospasm - Wheezing - Runny nose - Stomach symptoms like abdominal cramping In addition, a characteristic sign of an IgE mediated reaction are "wheal-and-flare" reactions, which are raised, red skin bumps. Patients having an anaphylactic reaction might also experience: - Blackouts - Nausea - Vomiting - Swollen areas - Low blood pressure - Rapid heart rate (tachycardia) - Rapid breathing (tachypnea) When evaluating for anaphylaxis, it is important to check the airways, breathing, circulation, and mental status as first steps.

Type I hypersensitivity reaction occurs when our body encounters an antigen, which it sees as harmful. This reaction happens in two stages: sensitization and effect. In the sensitization stage, our body comes into contact with the antigen without showing any symptoms. In the effect stage, our body encounters the antigen for a second time and treats it as a threat, triggering an allergic or immune response.

The other conditions that a doctor needs to rule out when diagnosing Type I Hypersensitivity Reaction are: - Lung diseases such as acute non-allergic asthma, chronic obstructive pulmonary disease (COPD), emphysema, or pneumothorax - Swallowing of foreign objects - Epiglottitis (inflammation in your throat) - Hereditary angioedema (swelling in some parts of the body) - Irritable bowel syndrome - Upper respiratory infections - Syncope (fainting) - Panic or anxiety attacks - Generalized urticaria (hives) caused by infection or hot or cold stimuli Moreover, some types of shocks mimic anaphylaxis, which can complicate diagnosis. These include: - Hypovolemic shock, due to things like a ruptured ectopic pregnancy, or systemic capillary leak syndrome - Cardiogenic shock (heart can't pump enough blood) - Distributive shock, like from sepsis - Obstructive shock such as from a blood clot in the lungs or cardiac tamponade Additionally, certain medications and conditions can cause reactions that look like but aren't anaphylaxis. For instance: - Fast infusion of the antibiotic vancomycin may lead to the 'red man syndrome' - Alcohol - Neuroendocrine tumors (carcinoid syndrome) - Perimenopause - Nonorganic diseases that need to be differentiated, such as psychosomatic episodes, or Munchausen stridor, or anaphylaxis in which the patient self-induces the reaction by purposely ingesting the offending agent

The types of tests that are needed for Type I Hypersensitivity Reaction include: - In-vitro tests: - Checking for elevated levels of serum tryptase - Checking for a higher count of eosinophils - Checking the levels of IgE - Allergen-specific IgE tests - Histamine level test - Flow cytometric basophil activation test (BAT) - In-vivo tests: - Skin test - Drug provocation test - Spirometry or pulmonary function tests - Challenges to check for airway hypersensitivity - Mucus sample tests (nasal smear or induced sputum) to check for eosinophils.

The treatment for Type I Hypersensitivity Reaction depends on the specific symptoms and cause of the reaction. For severe and life-threatening allergic reactions like anaphylaxis, immediate medical attention is required. This may involve positioning the patient lying down with raised legs and administering an injection of epinephrine (adrenaline) to reduce the severity of the reaction. In some cases, individuals with a history of severe allergic reactions may carry a prescription kit for self-treatment, which can include epinephrine, bronchodilators, antihistamines, and corticosteroids. Further treatment may involve beta-agonists, antihistamines, and glucocorticoids to control symptoms. For skin reactions like urticarial or angioedema, the treatment is similar to anaphylaxis, with the removal of the cause, antihistamines, and glucocorticoids for symptom relief. Other allergic conditions such as allergic asthma, allergic rhinitis, allergic conjunctivitis, allergic dermatitis, eczema, venom allergies, drug allergies, or food allergies may involve avoiding the allergen and using oral or topical antihistamines and glucocorticoids to manage symptoms. Allergen immunotherapy, also known as allergy shots, may be considered for individuals whose allergies significantly affect their life and have not responded to other treatments.

The side effects when treating Type I Hypersensitivity Reaction can include low blood pressure (hypotension), difficulty in breathing or lack of oxygen (hypoxia), and failure of the circulation system (distributive shock).

The prognosis for Type I Hypersensitivity Reaction can vary depending on the severity of the reaction. In general, these reactions don't last long and the risk of harm is low as long as symptoms are managed or the trigger is avoided. However, if conditions like angioedema, anaphylaxis, or severe asthma are not quickly recognized and treated, it can become a life-threatening situation within minutes. The risk of death from these conditions can increase with age, with adults being about 7 times more at risk than children. Black people have approximately a 75% greater risk compared to white people, and females have a 30% higher risk.

An allergist is the type of doctor you should see for Type I Hypersensitivity Reaction.