What Are Allergies?

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Allergies are basically an abnormal immune system response against normally harmless substances, called allergens. The allergic person’s body reacts by releasing chemicals that ultimately produce symptoms such as sneezing, runny nose, rash, or swelling. In some cases, allergies can even lead to life-threatening symptoms. The most common types of allergies include hay fever, food allergies, atopic dermatitis (eczema).

Allergies are among the most common reasons people visit the doctor.

Allergy Symptoms

In an allergic reaction, the body releases chemicals including histamine and leukotrienes. These chemicals affect the skin, respiratory system, digestive tract, and more, causing symptoms including (but limited to):

  • Sneezing
  • Runny nose/congestion
  • Rash
  • Itchiness
  • Hives
  • Swelling

The specific symptoms vary with the type of allergy.

For example, in atopic dermatitis, the main symptom is itching. Food allergies can produce skin symptoms including hives, swelling, itching, and redness, but may also have digestive symptoms such as nausea or diarrhea and respiratory symptoms.

Allergic rhinitis from pollen, molds, pet dander, and dust mites primarily yields respiratory symptoms such as sneezing, runny nose, itchy eyes, and nasal congestion. Contact dermatitis results in red, itchy, blistered skin.

In severe allergic reactions, there may be symptoms of anaphylaxis with swelling of the face, tongue, lips, throat, or limbs, hives, breathing problems, and low blood pressure. This is a medical emergency and immediate treatment is needed.


Allergens are normally harmless substances that lead to the development of allergy symptoms in those prone to allergies. These include things like pollens, latex, molds, animal dander, dust mites, certain foods, and certain medications.

You do not usually develop symptoms the first time you’re exposed to an allergen, but with later exposure, your body makes allergic antibodies (IgE) against the allergen. Re-exposure of the allergen leads to the allergen binding to immune cells and a cascade of events that ultimately result in the development of symptoms.

Allergens that travel through the air and enter your body through breathing are more likely to cause respiratory and nasal symptoms, while allergens that you would ingest may lead to gastrointestinal or systemic symptoms.

Why some people develop allergies to particular substances and others do not is unknown. Allergies sometimes run in families, and other times there will be no family history in someone with severe allergy symptoms. While allergies more commonly occur in childhood, you can develop them at any time in your life.


The diagnostic tests and criteria differ based on the type of allergy. The first step is keeping detailed notes about your symptoms, when they occur, and when you were exposed to possible allergens. Share these with your doctor to help with diagnosis.

Allergy testing can identify which allergens are responsible for your symptoms. For accuracy, this should only be done by a medical professional rather than using home tests.

The two types of testing are skin testing (prick/puncture and intradermal) and specific IgE (sIgE) blood testing. In cases of food allergy, the physician may decide to perform an oral food challenge. Asthma can be diagnosed with spirometry.


In general, patients with allergies need to avoid anything that leads to irritation and allergy symptoms. By being aware of your allergy triggers, you will be much less likely to have symptoms or allergic reactions.

For very mild allergy symptoms, over-the-counter antihistamines may be all the treatment that is needed. You might also try a saline rinse or spray for nasal symptoms.

If over-the-counter medications are not providing you allergy relief, talk with your doctor about prescription medications to address your allergy symptoms. The types of medication will vary depending on the type of allergy, such as topical steroid creams for atopic dermatitis and oral decongestants and antihistamines for allergic rhinitis. Take every drug as prescribed so it can be effective and to avoid side effects.

If your allergy puts you at risk for a severe anaphylactic reaction, you may need to carry injectable epinephrine.

Cases that are not helped with the above treatments may require other options, such as allergy shots.

A Word From Verywell

Managing allergies can be very frustrating. It may seem like a difficult task to avoid triggers and manage a complicated treatment regimen. By developing a trusting and communicative relationship with your healthcare team, you can develop a treatment regimen that is manageable and lessen the impact of allergies on your life.

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Article Sources
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  1. American Academy of Allergy Asthma & Immunology. Allergic Reactions.

  2. Kołodziejczyk K, Bozek A. Clinical Distinctness of Allergic Rhinitis in Patients with Allergy to Molds. Biomed Res Int. 2016;2016:3171594. doi:10.1155/2016/3171594

  3. American Academy of Allergy Asthma & Immunology. All About Allergy Testing.

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