What happens to the body during an allergic reaction?

A woman having a runny nose due to an allergic reaction

Key takeaways

  • An allergic reaction occurs when the body reacts to an allergen, which is a usually harmless substance that the body's immune system recognizes as a foreign agent.
  • A series of things happen to the body during an allergic reaction, including the appearance of hives, gastrointestinal symptoms, runny nose, and anaphylactic shock.

The immune system produces five types of antibodies, namely, IgG, IgM, IgA, IgD, and IgE. These antibodies (also called immunoglobulin) are involved in the immune response. They are protective proteins produced by the immune system in response to a foreign substance (called an antigen).

The antibody involved in allergic reactions is IgE. When you are allergic to a substance, your body forms an IgE antibody against that substance. When that substance comes into contact with your body, the IgE launches an attack against it, causing a nasty reaction called an allergic reaction.

Recently, allergy cases have been on the rise in the industrialized world. According to the American Academy of Allergy, Asthma, and Immunology, in 2010, 11.1 million visits to physician offices resulted in a primary diagnosis of allergic rhinitis.  

In this article, we will discuss all about allergy, and what happens to the body during an allergic reaction.

Meaning of allergy and allergic reaction

Allergies are the body’s natural reaction to anything it views as “a foreign invader”. An allergy is a condition that occurs when the immune system reacts abnormally to a foreign agent. 

The role of the body’s immune system is to fight against foreign agents, particularly infectious agents like bacteria and viruses. However, in the case of allergies, the body reacts to normally harmless substances called allergens, e.g., pollen from plants. 

If a person allergic to pollen comes into contact with it, their immune system will react to the pollen. This is known as an allergic reaction. Allergic reactions cause symptoms in various parts of the body, such as the sinuses, the lungs, the nose, the ears, the throat, the skin, and the stomach lining. 

What happens during an allergic reaction

A series of events happen during an allergic reaction, including the appearance of hives on the body, experiencing runny nose, and having anaphylactic shock.

When people are prone to an allergen, e.g., pollen, their immune system identifies pollen as an invader. When such people are exposed to pollen for the first time, their bodies respond by producing IgE, which are allergic antibodies.

The role of the IgE antibody is to find the allergens and get rid of them from the body. This results in the release of a chemical called histamine. Histamine is stored in mast cells (a type of immune system cell) located in the gut, lungs, skin, nose, mouth, and blood. 

Histamine plays a central role in the development of several allergic diseases, such as allergic rhinitis, atopic dermatitis, and allergic asthma. It causes the allergy symptoms experienced during an allergic reaction.

Once released from its granules, histamine causes different effects on the body, such as the dilation of blood vessels, contraction of smooth muscles of the uterus, lungs, and stomach, an increase in heart rate, and stimulation of gastric acid secretion in the stomach.

The following happens to your body when you have an allergic reaction:

1. Hives

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One of the things that happens during an allergic reaction is the appearance of hives. Hives appear as raised spots that are pink, red, or skin-colored. They are itchy and vary in size and shape. 

Hives appear when the body releases histamine as a defense mechanism. The released histamine causes the surrounding blood cells to dilate and increase in permeability. Blood fluid, along with white blood cells and plasma proteins, leaks through the blood vessels, causing hives to appear.

Hives typically don’t last for long; they usually disappear within 24 hours.

2. Digestive problems

One of the things that happens during an allergic reaction is digestive issues. People who are allergic to food substances often experience digestive problems during an allergic reaction. This is because the antibodies their body has developed against that food substance (the allergen) struggle to invade the substance. 

Common digestive problems experienced during an allergic reaction include nausea and vomiting, abdominal pain, and diarrhea.

Most of these allergy symptoms occur within two hours of ingesting the food substance. In rare cases, the allergic reaction may start after about 4 to 6 hours.

3. Runny or congested nose

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The nose does a great job of filtering the air that passes through it every second. However, when the nostrils get hit by an allergy, the immune system overreacts, causing a series of allergic reactions.

The mast cells in the nasal cavity release the chemicals leukotrienes and histamines to fight an allergen. The release of these chemicals can cause the swelling of blood vessels in the nasal cavity and an increase in mucus production, which causes nasal congestion and a runny nose.

4. Anaphylactic shock

Anaphylactic shock can occur in severe cases of allergy. Anaphylaxis occurs when the immune system releases a series of chemicals that can cause the body to go into shock.

Blood pressure declines abruptly during an anaphylactic shock, and the airways narrow, disrupting normal breathing. Anaphylaxis is dangerous. It can cause serious complications that are potentially life-threatening if not treated immediately.

Anaphylactic shock can cause shortness of breath, swelling of the tongue and throat, difficulty breathing, gastrointestinal problems, a drastic drop in blood pressure, and red, itchy skin. The most common anaphylactic reactions are reactions to food, latex, medications, and insect stings.

Other symptoms a person may experience during an allergic reaction include watery eyes, tissue swelling, and constriction of the bronchi.

Causes of allergies

Experts have suggested that one of the leading causes of the increasing prevalence of allergies is hygiene. According to this hypothesis, the living conditions in some parts of the world are too clean. The result is that children don’t get exposed to germs that will train their immune systems to differentiate between harmful and harmless substances. 

Another suggested cause of the increase in allergies is antibiotics and acetaminophen. Studies have shown that the increased use of antibiotics has led to a rise in health conditions like allergies and asthma. 

Experts are not exactly sure why some people experience allergies, but they have identified some common causes, which include:

  • Certain foods, particularly soy, shellfish, fish, eggs, peanuts, and other eggs
  • Airborne allergens like dust mites and pollen
  • Medications like Penicillin
  • Stings from insects like wasps and bees

What to do when a person has an allergic reaction

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If you or someone close to you has an allergic reaction, seek emergency care immediately.

If it is not a first-time incidence, the chances are high that the person knows what is causing the reaction. Check if the person is wearing an allergy bracelet or ask them what they are allergic to.

If the allergen is a substance that can be gotten rid of right away, e.g., pollen, go ahead and get rid of it immediately. If the person is not breathing, quickly call for help, and give them CPR while the medical team arrives. 

If the person is conscious, place them in a sitting position and encourage them to take deep, slow breaths. If there is an epinephrine auto-injector (EpiPen), use it at the onset of the symptom. An anti-histamine medication can also help relieve the symptoms.

Note that this is only a first-aid tip. The person still needs to get medical attention from a health professional.