What Are Allergies?

Contributor: Hannah Brooks. Lesson ID: 12523

You don't have a cold or flu, but you are coughing and sneezing and going through tissues like there's no tomorrow. Learn about the immune system's amazing work as it fights off those nasty allergens!


Life Science

learning style
Auditory, Visual
personality style
Grade Level
Middle School (6-8), High School (9-12)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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Ahhh, springtime! New flowers, budding trees, baby animals, warm weather, sneezing, itchy, watery eyes, sore throat. Uh oh, it's allergy season!

  • Why?
  • Have you noticed that you may sneeze more in the spring?

That occurs because there are more substances in the air that cause an immune response in your body called an allergy.

allergy sign

Your immune system usually functions to fight off invading germs and infections, but sometimes it can be confused by substances like pollen, mold, insect stings, and medications.


These substances are called allergens, because they cause allergy symptoms like watering eyes, a running nose, and sneezing. Allergens are considered antigens, or foreign particles, in the immune system because they cause the immune response in the body.

When an allergen is received by the body, it is met with specialized immune system cells that identify it as a foreign invader. These cells start producing antibodies, proteins that the body uses to fight pathogens. These antibodies help recognize the allergen in the future, and drive the response that leads to allergy symptoms.


Antibodies, shown above, attach to mast cells, also known as white blood cells, another immune system cell responsible for protecting the body. The antibodies can overwhelm the white blood cells, destroying them. White blood cells release a chemical, called histamine, that leads to the loosening of blood vessels causing allergy symptoms like itching, hives, and sneezing! Notice how the histamine is released by the mast cell in the image below. It then moves to different parts of the body, causing allergy symptoms.


Some people have more serious allergic responses, and can experience anaphylaxis. This is a reaction that builds over an extended time, becoming worse with age. The allergic reaction occurs quickly, sometimes even within a few minutes. The individual can experience large patches of hives and have issues with breathing. If untreated, it can cause organ damage due to a loss of oxygen. Anaphylactic shock occurs when the breathing airway swells and becomes closed. This leads to total loss of oxygen and can result in death.

anaphylactic shock

Allergies can be treated using daily medication, avoidance of triggers, and using epinephrine pens (Epi-pens). Treatment depends on the type and severity of the allergy. In the next lesson of this Allergies series, found in the right-hand sidebar under Related Lessons, you will learn more about types and treatment of different allergies.

Allergies can be very unpleasant, causing anything from daily irritation to more severe reactions. All allergies are triggered by substances known as allergens found in our environment. These substances cause immune reactions in the body that lead to symptoms like sneezing, itching, and watery eyes. In some people, these reactions can even lead to anaphylactic shock where the airway closes up.

  • What allergies do you have?
  • How do your allergies impact your life?
  • If you don't have any allergies, what allergies do family members have?

Make a short list of some of the allergens that irritate you on a sheet of paper.

Then, move on to the Got It? section, where you will learn more about the immune response in allergies.

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