What is Allergic Reactions?

Allergic reactions are sensitivities to substances called allergens that come into contact with the skin, nose, eyes, respiratory tract, and gastrointestinal tract. They can be breathed into the lungs, swallowed, or injected.


The symptoms of an allergic reaction can vary from mild to severe. If you become exposed to an allergen for the first time, your symptoms may be mild. These symptoms may get worse if you repeatedly come into contact with the allergen.

Symptoms of Mild Allergic Reactions

  • Hives (itchy red spots on the skin)
  • Itching
  • Nasal congestion (known as rhinitis)
  • Rash
  • Scratchy throat
  • Watery or itchy eyes
allergic reaction

Severe Allergic Reactions

  • Abdominal cramping or pain
  • Pain or tightness in the chest
  • Diarrhea
  • Difficulty swallowing
  • Dizziness (vertigo)
  • Fear or anxiety
  • Flushing of the face
  • Nausea or vomiting
  • Heart palpitations
  • Swelling of the face, eyes, or tongue
  • Weakness
  • Wheezing
  • Difficulty breathing
  • Unconsciousness

A severe and sudden allergic reaction can develop within seconds after exposure to an allergen. This type of reaction is known as anaphylaxis and results in life-threatening symptoms, including swelling of the airway, inability to breathe, and a sudden and severe drop in blood pressure. If you experience this type of allergic reaction, seek immediate emergency help. Without treatment, this condition can result in death within 15 minutes.


The most commonly ordered types of allergy tests are

  • Skin tests
  • Challenge (elimination-type) tests
  • Blood tests

A skin test involves applying a small amount of a suspected allergen to the skin and watching for a reaction. The substance may be taped to the skin (patch test), applied via a small prick to the skin (prick test), or injected just under the skin (intradermal test).

A skin test is most valuable for diagnosing

  • Food allergy
  • Mold, pollen, and animal dander allergy
  • Penicillin allergy
  • Venom allergy (such as mosquito bites or bee stings)
  • Allergic contact dermatitis (a rash you get from touching a substance)
  • Challenge testing is useful in diagnosing food allergies. It involves removing a food from your diet for several weeks and watching for symptoms when you eat the food again.

A blood test for an allergy checks your blood for antibodies against a possible allergen. An antibody is a protein your body produces to fight harmful substances. Blood tests are an option when skin testing isn’t helpful or possible. Prevent an Allergic Reaction


Once you identify your allergy, you can:

  • Avoid exposure to the allergen.
  • Seek medical care if you are exposed to the allergen.
  • Carry medications to treat anaphylaxis.

You may not be able to avoid an allergic reaction completely, but these steps can help you to prevent future allergic reactions.

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Frequently Asked Questions

How long does an allergic reaction last?

They can take from a few hours to a few days to disappear. If exposure to the allergen continues, such as during spring pollen season, allergic reactions can last for longer periods, such as a few weeks or months.

What are the 4 types of allergic reactions?

Four different types of allergic reactions are immediate, cytotoxic, immune-mediated, and delayed hypersensitivity reactions. Allergic reactions occur when the body's immune system reacts to a substance it considers harmful, called an allergen.

What are the signs that you're having an allergic reaction?

The most common signs and symptoms of an allergic reaction include coughing, difficulty or irregular breathing, wheezing, itchy throat or mouth, and difficulty swallowing. Nausea, vomiting, abdominal pain, and diarrhea. Red itching, bumps or bumps on the skin (hives), and redness of the skin.