About Allergies
About Allergies

A substance that causes an allergic reaction is called an allergen. Many allergies are everyday substances that are harmless to most people. However, anything can be an allergen if the immune system has a specific type of adverse reaction to it.

One role of the immune system is to eliminate harmful substances in the body. If a person is allergic to a substance, their immune system will react as if the substance is harmful and try to destroy it.

More than 50 million people in the United States experience an allergic reaction each year. This reaction can lead to symptoms such as swelling. If the inflammation affects the airways, it can be life-threatening.

In this article, learn about the risk factors, symptoms, and treatments associated with allergies.

What is an Allergy?

Allergies occur when a person’s immune system overreacts to substances that are normally harmless.

The first time a person is exposed to an allergen, they usually do not experience a reaction. It often takes time for the immune system to develop sensitivity to a substance.

Over time, the immune system learns to recognize and remember the allergen. As it does this, it starts making antibodies to attack it when exposed. This construct is called sensitivity.

Some allergies are seasonal. For example, hay fever symptoms may peak between April and May, when tree and grass pollen counts are high in the air. A person may experience more severe reactions as the pollen count increases.


Allergic reactions cause inflammation and irritation. However, specific symptoms will depend on the type of allergen. For example, allergic reactions may occur in the gut, skin, sinuses, airways, eyes, or nasal passages.

Below are some of the triggers and symptoms that can develop in people allergic to them.

Dust and pollen

  • a blocked or congested nose
  • swollen and watery eyes
  • a runny nose
  • itchy eyes and nose
  • a cough


  • vomiting
  • a swollen tongue
  • shortness of breath
  • stomach cramps
  • tingling in the mouth
  • rectal bleeding, mainly in children
  • swelling of the lips, face, and throat
  • itchiness in the mouth
  • diarrhea

Insect stings

  • wheezing
  • hives, or a red and very itchy rash that spreads across the body
  • itchy skin
  • a cough
  • significant swelling at the site of the sting
  • shortness of breath
  • restlessness
  • dizziness
  • a sudden drop in blood pressure
  • chest tightness


  • a rash
  • wheezing
  • swelling of the tongue, lips, and face
  • itchiness

If symptoms become severe, anaphylaxis can develop.

Anaphylaxis Aymptoms

Anaphylaxis is the most severe form of allergic reaction. This is a medical emergency and can be life-threatening. Anaphylaxis can develop rapidly, with symptoms appearing within minutes or hours of exposure to the allergen.

Research shows that anaphylaxis most commonly affects the skin and respiratory system.

Some symptoms include:

  • hives, flushing, and itchiness
  • changes in heart rate
  • difficulty breathing
  • low blood pressure
  • swelling
  • dizziness and fainting
  • wheezing
  • loss of consciousness

Recognizing these symptoms can be crucial to receiving timely treatment.


When an allergic reaction occurs, the allergen binds to antibodies that the body produces called immunoglobulin E (IgE). Antibodies fight foreign and potentially harmful substances in the body.

Once an allergen binds to IgE, certain types of cells – including mast cells – will release chemicals that trigger the symptoms of an allergic reaction.

Histamine is one of these chemicals. This causes the muscles in the walls of the airways and blood vessels to tighten. It also directs the nasal lining to produce more mucus.

Common Allergens

Potential allergens can appear almost anywhere.

In theory, a person can be allergic to any food. Certain ingredients – such as gluten, a protein in wheat – can also trigger the reaction.

The eight foods most likely to cause allergies are:

  • eggs, especially the whites
  • crustacean shellfish
  • fish
  • wheat
  • milk
  • tree nuts
  • peanuts
  • soy

Some other common allergens include:

  • pet fur, dander, skin flakes, or saliva
  • household chemicals
  • mold and mildew
  • cockroaches, caddisflies, midges, and moths
  • metals, such as nickel, cobalt, chromium, and zinc
  • medications, such as penicillin
  • insect stings and bites
  • plant pollens
  • latex

Prevention and Precautions

There is no way to prevent or cure allergies, but it is possible to prevent a reaction or manage symptoms if a reaction occurs.

People who are at risk of allergies should:

  • Take steps to avoid exposure to known allergens.
  • Carry two auto-injectors and know how to use them properly.
  • Tell friends, relatives, colleagues and others about the allergy and the use of the auto-injector.
  • Consider wearing a medical identification bracelet with allergy details.
  • Get allergy testing done to find out what to avoid.
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