How Do Allergies Work?

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Allergies work by triggering the immune system in response to an allergen. Allergens are substances the body mistakes as dangerous. As a result, the body makes antibodies to fight them. 

The production of antibodies results in allergy symptoms, like runny nose, itchy eyes, cough, and hives. The most severe allergic reaction is anaphylaxis. This reaction is a life-threatening medical emergency that can cause a person to collapse or stop breathing.

This article explains how allergies develop and what happens in the body when a reaction is life-threatening.

Person with white skin and brown hair sits on a couch blowing their nose

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The Process

Allergies happen when you come in contact with an allergen. Your immune system produces antibodies, and when triggered, the antibodies cause the release of histamines.

An Allergen Enters Your Body

For people with allergies, their immune system recognizes allergens as harmful. Depending on the source, allergens may enter your body through your respiratory system, digestive tract, or skin.

Common allergens include:

When you have allergies and allergens enter your body, your body responds by attacking the substance. 

Antibodies (Immunoglobulin) Are Produced 

When your body detects an allergen, it responds by making a specific kind of antibody called immunoglobulin E (IgE).

These antibodies are specific to a particular allergen. That means you may be allergic to one type of pollen but not another.

Immunoglobulin

Immunoglobulins are antibodies that B-cells produce. The body has five types of immunoglobulins, including IgE, which is responsible for the allergic response.

Once your body makes an antibody to an allergen, you'll likely continue to have the same reaction to that allergen the next time you come in contact with it.

Histamines Are Released

Histamine is a chemical in the body that sends messages to the immune system. Your immune cells and white blood cells release histamine when exposed to an allergen. These histamines cause the symptoms you experience, like itchy eyes, scratchy throat, runny nose, and cough.

Antihistamines are medications that block histamines and, thus, reduce your allergy symptoms. Most antihistamines are available over the counter (OTC), without a prescription. They're also available in prescription strength. 

Histamine Toxicity

Histamine toxicity (also called scombroid poisoning) is different from histamine intolerance and allergies. Histamine toxicity is caused by eating spoiled fish. The primary toxic agent is histidine, which breaks down into histamine. Symptoms occur quickly, usually within an hour of eating fish. They include:

  • Rash
  • Flushing
  • Headache
  • Diarrhea

Symptoms often improve quickly after treatment with antihistamines.

Anaphylaxis

Anaphylaxis is a severe, life-threatening allergic reaction that affects multiple systems of the body. In adults, it usually results from insect bites or stings and medications.

Symptoms of Anaphylactic Shock

Symptoms of anaphylaxis come on fast and include:

  • Itching
  • Rash
  • Swollen throat
  • Loss of consciousness
  • Hoarse voice
  • Difficulty swallowing
  • Wheezing
  • Shortness of breath
  • Vomiting
  • Diarrhea
  • Sense of panic

What to Do

If you notice signs of anaphylaxis, it's crucial to seek medical attention immediately. Anaphylaxis is a life-threatening emergency. So, it's appropriate to call 911 if you or someone you're with are experiencing symptoms.

If you have a history of severe allergic reactions, your healthcare provider will likely prescribe epinephrine (commonly called an EpiPen) for you to keep on hand.

This medication is a form of adrenaline. It alleviates the symptoms of anaphylaxis by relaxing the smooth muscles in the bronchi in the lungs. This process helps you breathe again. It can also treat anaphylactic shock and symptoms before they progress to anaphylactic shock.

When to Talk to Your Healthcare Provider

Allergies can range from a minor nuisance to a life-threatening reaction, so how you cope with allergies will depend on how severe your allergies are. If your allergies are only mildly bothersome, you may be able to manage them by avoiding allergens and taking OTC antihistamines.

On the other hand, you may want to see a healthcare professional if:

  • Your allergies disrupt your life.
  • It is unclear what allergens are affecting you.
  • You have symptoms of a more severe allergic reaction.

When to Seek Emergency Medical Care

If you ever experience symptoms of anaphylaxis, call 911 immediately.


Summary

An allergic reaction occurs when you come in contact with an allergen. Your immune system produces antibodies, and when triggered, the antibodies cause the release of histamines and other mediators.

Once your body makes an antibody to an allergen, you'll likely continue to have the same reaction to that allergen the next time you come in contact with it.

If your allergies are only mildly bothersome, you may be able to manage them by avoiding allergens and taking OTC antihistamines.

Anaphylaxis is a severe, life-threatening allergic reaction that affects multiple systems of the body. It usually results from insect bites or stings and medications. If you notice signs of anaphylaxis, it's crucial to seek medical attention immediately.

A Word From Verywell

If you have allergies, understanding how they work can help you avoid or limit your exposure and manage your symptoms. Often, people with allergies find relief from antihistamines. However, if avoiding allergens and OTC treatments aren't helping, you may benefit from a visit to your healthcare provider. They'll be able to diagnose your allergies and develop a treatment plan.

Frequently Asked Questions

  • How long does it take for an allergic reaction to occur?

    An allergic reaction can occur moments to hours after exposure. Severe allergic reactions tend to come on quickly.

  • How long does an allergic reaction last?

    Allergic reactions typically last as long as you remain exposed to the allergen. For example, if you are allergic to pollen, you'll likely have persistent symptoms when pollen counts are high.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Johns Hopkins Medicine. Allergies and the immune system.  

  2. U.S. National Library of Medicine. Allergen.

  3. Traylor J, Mathew D. Histamine toxicity. In: StatPearls. StatPearls Publishing; 2021.

  4. American Academy of Allergy, Asthma, and Immunology. Anaphylaxis.  

  5. U.S. National Library of Medicine. Allergic reactions.