What Are Allergens?

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Allergens are substances that cause the body to produce an allergic reaction. When you have allergies, your body mistakenly reacts to specific substances it detects as dangerous (allergens) by making antibodies to fight them. Allergic reactions are symptoms that result from your body creating these antibodies.

Allergens can be airborne or can arise from contact with your skin, from medications, or from food. Depending on the type, they may enter your body through your respiratory system, skin, or digestive tract.

This article explains types of allergens, how they work, and their risks. It also covers how to diagnose allergies and treat exposure to allergens.

Blurred person holds tissue to their nose in response to ragweed

Roy Morsch / Getty Images

How Allergens Work

When you develop an allergic reaction to a substance, your body treats that substance (allergen) as a germ, or threat. Your body then produces an immune response against the allergen. Instead of producing a healthy immune response, it creates IgE antibodies against the allergens.

If you have allergies, your body begins making antibodies when you expose it to an allergen. Those antibodies attach to specific cells in your body. In the future, when you come into contact with the same allergen, those cells release histamines, which produce symptoms like sneezing, itching, and watery eyes.

Allergy Statistics

Allergies are prevalent. In fact, according to the Allergy and Asthma Foundation of America:

  • More than 50 million Americans have allergies.
  • Allergies are one of the most common conditions affecting children.
  • Hay fever affects more than 5 million children and more than 19 million adults.
  • About 32 million people have food allergies.

The reason some people but not others develop allergies in response to specific allergens isn't fully understood, but allergies tend to run in families


Different types of allergens affect people in different ways. For example, some cause respiratory symptoms, while others result in skin rashes or gastrointestinal upset. Less frequently, they can also cause a life-threatening allergic reaction.

Airborne Allergens

Airborne allergens are those that you breathe into your respiratory system. Seasonal allergies and hay fever fall under this category. These types of allergies usually result in nasal allergy symptoms (allergic rhinitis) and/or eye symptoms (allergic conjunctivitis).

Common airborne allergens are:

Climate Change and Allergens

Climate change is resulting in higher pollen counts and longer pollen seasons. That's because higher temperatures, changes in precipitation patterns, and higher carbon dioxide in the atmosphere increase the risk of exposure to allergens.

Skin Allergens

Skin rashes are a typical response after allergens come into contact with your skin. These allergies are known as allergic contact dermatitis. Common allergens in this category include:

Food Allergens  

Food allergens can range from mild to severe. When they're severe, they can cause anaphylactic reactions, which can be fatal. 

Although it's possible to be allergic to any food, some foods are more common allergens than others. The Food Allergy Safety, Treatment, Education, and Research (FASTER) Act of 2021 identifies the following eight foods as major food allergens:

Medication Allergens

Drug allergens may cause skin rashes, wheezing, itching, and anaphylaxis. It's possible to have an allergic reaction to any medication. However, the most common drug allergens are:

  • Penicillin and similar antibiotics
  • Nonsteroidal anti-inflammatory drugs (NSAIDs, such as aspirin, Advil or Motrin, which are ibuprofens, or Aleve, which is a naproxen)
  • Sulfa drugs (often used to treat urinary tract infections, bronchitis, or eye infections)
  • Anticonvulsants (used to treat epileptic seizures)
  • Chemotherapy medication (used to kill cancer cells)


Exposure to allergens can result in a wide variety of symptoms. Pollen and other airborne allergies most commonly result in nasal and respiratory symptoms, while contact dermatitis often shows up as a skin rash. However, any allergen can cause any allergic symptoms.

Common allergy symptoms include:


Less commonly, an allergen can produce a severe allergic reaction called anaphylaxis. This life-threatening reaction causes swelling in the throat and difficulty breathing. Onset is short—usually five to 30 minutes from exposure to an allergen.

Anaphylaxis is a medical emergency that requires immediate attention. Epinephrine is necessary to treat anaphylaxis. If you have a history of this severe reaction, your healthcare provider will usually prescribe this drug for you to keep at home (called an EpiPen).


Most of the time, allergens are a nuisance. However, exposure to them can result in more serious complications. Some risks of allergen exposure are:

  • Asthma: This is a chronic lung condition in which the lungs react by closing when exposed to certain triggers. Having allergies is a known risk factor for developing asthma. 
  • Severe allergic reactions: These might occur when you're exposed to an allergen. In addition, anaphylaxis can occur rapidly and without warning.
  • Chronic infections: Certain infections, like sinus infections, are more common in people with allergies.

Allergen Tests

Allergists usually perform allergen testing in their offices. They may perform skin tests or blood tests to diagnose your allergies.

  • Skin test: These tests involve pricking or scraping the skin with an allergen to see if there's a reaction. Another variation of a skin test is an intradermal test, in which your healthcare provider injects a minimal amount of allergen under the skin with a small needle.
  • Blood test: Drawing blood to test for antibodies is another method of checking for allergies.


There is a wide variety of treatment options for exposure to allergens. The best treatment is to avoid the allergen. However, sometimes that's not possible or reasonable. Typical allergy treatments include:


When you have allergies, your body mistakenly reacts to specific allergens as dangerous substances by making antibodies to fight them. Allergic reactions are symptoms that result from your body creating these antibodies. Allergies are common, affecting more than 50 million Americans.

Types of allergens include those that are airborne or those that arise from contact with your skin, from food, and from medications. Common allergy symptoms include runny nose, congestion, cough, and sneezing, among others. Less commonly, an allergen can produce a severe allergic reaction called anaphylaxis. 

Allergy treatment involves avoiding the allergen and over-the-counter (OTC) medications. If you're unsure what's causing your allergies, speak with a healthcare provider. They can better assist you in determining what you're allergic to.

A Word From Verywell

If you have allergies, avoid allergens as much as possible. Sometimes identifying which substances cause reactions is straightforward. For example, if after you pet a cat you immediately get itchy eyes and start sneezing, you are likely to be allergic to a cat's saliva, urine, or skin cells. Other times, it can be more challenging to determine what the culprit is that's causing your symptoms.

An allergist can help you pinpoint which allergens are causing you trouble by performing an allergy test. They can also help you figure out the best way to manage your allergy symptoms.

14 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. U.S. National Library of Medicine. Allergens.

  2. National Center for Biotechnology Information, U.S. National Library of Medicine. Allergies: Overview.

  3. Allergy and Asthma Foundation of America. Allergy facts and figures.

  4. National Health Service. Causes: Allergic rhinitis.

  5. Centers for Disease Control and Prevention. Allergens and pollen.

  6. Asthma and Allergy Foundation of America. What is an allergic skin condition?.

  7. U.S. Food and Drug Administration. Food Allergies.

  8. American College of Allergy, Asthma, and Immunology. Drug allergies: Overview.

  9. American College of Allergy, Asthma, and Immunology. Allergy symptoms.

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

  11. American Lung Association. Asthma risk factors.

  12. Cleveland Clinic. Chronic sinusitis.

  13. American College of Allergy, Asthma, and Immunology. Testing and diagnosis.

  14. Asthma and Allergy Foundation of America. Allergy treatment. Updated March 2018.

By Kathi Valeii
As a freelance writer, Kathi has experience writing both reported features and essays for national publications on the topics of healthcare, advocacy, and education. The bulk of her work centers on parenting, education, health, and social justice.