What are Allergies?

Allergies are disorders of the immune system. More specifically, they are an overreaction of an individual’s immune system in response to a foreign, or “non-self,” substance that is perceived as harmless by most other people’s bodies. Allergies are one of the most common chronic conditions, affecting up to 50% of the population in some areas of the industrialized world, according to the World Allergy Organization.

What Causes Allergies?

Allergies are caused by a hyperactive immune system response. People with allergies produce an immune response to a substance in the environment that is typically harmless.

Anyone with a family or personal history of allergies is at risk, but environmental factors can also play a role. Also, those with a medical history significant for asthma have a higher risk of suffering from allergies. Hormones, stress, smoke, perfume, or environmental irritants may also play a role in the development or severity of allergies.

The Immune System:

The immune system is the body’s coordinated defense against infectious organisms and other potentially harmful invaders, called antigens. Antigens can be found on the surface of living and non-living matter such as: cells, viruses, fungi, bacteria, toxins, chemicals, drugs, and foreign particles (such as a splinter). During an immune response, the immune system recognizes and reacts to antigens by producing protective proteins, called antibodies (also termed immunoglobulins). These antibodies adhere to specific antigens, making it easier for immune cells to identify and destroy the foreign invader.

The Immune System’s Role in the Allergic Response:

Allergies are disorders of the immune system. An allergic reaction is caused by a hypersensitive immune system response to certain antigens in the environment, called allergens, which most other people’s bodies perceive as being harmless.

Some of the most common allergens include:

  • Pollen
  • Dust
  • Food
  • Insect venom
  • Animal dander
  • Mold
  • Medications
  • Latex

The immune system overreacts to the antigens by producing Immunoglobulin E, or IgE, antibodies. These antibodies travel to cells that release histamine and other chemical mediators, which cause allergy symptoms to occur. The human body carries out an allergic cascade in three stages: sensitization, “early-phase,” and “late-phase.”

Stage 1 – Sensitization

When a person comes into contact with an allergen for the first time, no allergic reaction occurs. Instead, the immune system undergoes the process of sensitization, in which it prepares itself for future encounters with the foreign invader.

In a series of steps, the immune system breaks apart the antigen, presents the fragments to immune cells, and produces an antibody that is specific to that antigen. This antibody is called immunoglobulin E, or IgE. A person who has created IgE antibodies specific to an antigen is referred to as having become “sensitized” to that antigen. The specificity of IgE antibodies is the reason people can be allergic to one substance, yet not another.

To conclude the sensitization stage, allergen-specific IgE antibodies attach to the surface of mast cells. Mast cells are a type of leukocyte, or white blood cell, commonly known as the “master regulators” of the immune system. They can be found in most tissues of the body and are strategically placed in locations that are in close contact with the external environment, such as skin, airways, and intestines, to aid in early recognition of allergens.

Stage 2 – “Early-phase”

When a person is re-exposed to a substance that he or she is allergic to, allergen-specific IgE antibodies recognize and bind to that allergen. Mast cells are stimulated when an abundance of the invading antigen cross-link and bind to the IgE located on its surface. Activation of mast cells results in the rapid release of histamine and other inflammatory substances, called mediators. Inflammatory mediators bind to receptors on target cells which leads to dilation of blood vessels, constriction of bronchioles, excessive mucus secretion, and other symptoms of allergy. Most people begin to experience “early-phase” allergy symptoms, such as sneezing, wheezing, itchy eyes, runny nose, cough, and hives within one hour after being exposed to an allergen.

Stage 3 – “Late-phase”

The “late-phase” allergic response typically begins 2-6 hours after exposure to an allergen and reaches a peak approximately 6-9 hours after. The activated mast cells attract many other inflammatory cells to the site, including eosinophils, basophils, neutrophils, and lymphocytes. Similarly to mast cells, these inflammatory cells release toxic chemicals that irritate the body, and can even cause tissue damage. “Late-phase” allergy symptoms, such as nasal congestion and continuous mucus production, often resolve 24-48 hours post-exposure.
The merging of “early-phase” and “late-phase” reactions can result in a severe allergic response.

Types of Allergies

There are many different types of allergies, all of which can cause varying symptoms and may require different treatments.

Seasonal Allergies

While the spring season is the most common time for seasonal allergies, they can also occur during the summer, fall, and winter months.

Food Allergies

Also known as food intolerances, often lead to an unpleasant reaction after eating or drinking an offending substance. Common food allergies include:

  • Nuts
  • Milk
  • Fish
  • Eggs
  • Wheat
  • Soy
  • Casein
  • Sulfite

Pet Allergies

Animals with dander, such as dogs and cats, often provoke pet-related allergies.

Insect Sting Allergies

Insects that sting – such as bees, wasps, hornets, fire ants, and yellow jackets – can cause an allergic reaction in some people.

Plant Allergies

Allergies to plants such as poison ivy, poison oak, and poison sumac are often due to the plant’s sap (urushiol).

Hay Fever

This is an allergic response to environmental triggers such as pollen grains.


Additional allergies can include the following:

  • Sun, or ultraviolet radiation
  • Mold
  • Medications (such as penicillin or aspirin)
  • Cosmetics
  • Nickel
  • Dust
  • Chemicals
  • Latex

Signs and Symptoms of Allergies

Allergy symptoms and their severity can be unpredictable; symptoms often vary from person to person. One person may not always experience the same symptoms during every reaction to the same allergen.

Common symptoms of allergies include:

Food allergies can also cause stomach cramps, vomiting, diarrhea, tingling in the mouth, or facial swelling.

Insect stings can also cause local swelling, redness, and pain.

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Diagnosing Allergies

Diagnosing an allergy requires careful consideration of multiple factors and is not always a straightforward process. Therefore, allergists undergo specialized training to be able to accurately diagnose and effectively treat allergies. Allergists use a person’s medical history and physical exam findings in conjunction with an appropriate allergy test to determine what a person is, as well as what he/she is not, allergic to. Although skin tests are used more frequently, blood tests can also be used to confirm an allergy.

Allergy Treatment and Prevention

A medical specialist can help you diagnose the cause and prescribe appropriate treatment for your allergies.

There is no cure for allergies. There are certain medications (both over-the-counter and prescription) you can take to reduce your symptoms and ease discomfort.

Staying away from the offending substance can reduce the chance that an allergic reaction will occur.

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If you have a severe allergy, it is especially important to wear a medical alert bracelet or necklace, and carry an auto-injector device containing epinephrine (adrenaline).

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When Should I Call a Doctor?

If your allergy symptoms continue despite treatment, or if you have any questions about your allergies, follow up with a medical specialist.

Emergency Warning Signs: Anaphylaxis

Anaphylaxis is a severe and potentially life-threatening allergic reaction that typically affects more than one part of the body at a time. The most common anaphylactic reactions are to foods, insect stings, medications, and latex. Symptoms tend to arise within seconds to minutes after exposure. During anaphylaxis, a flood of toxic chemicals are released by inflammatory cells of the immune system, which can cause a person’s body to go into shock.

Signs and symptoms of anaphylaxis include:

  • Sudden decrease in blood pressure
  • Narrowing of airways, causing breathing difficulties
  • Rapid, weak pulse
  • Chest tightness
  • Skin rash
  • Nausea and vomiting
  • Diarrhea
  • Dizziness, lightheadedness, or faintness
  • Tingling in the hands, feet, lips, or scalp
  • Cyanosis (pale or blue coloring of the skin)

Anaphylaxis can be fatal without immediate medical treatment, including an injection of epinephrine (adrenaline); head for the emergency room if you are experiencing symptoms of anaphylaxis.