Allergies are your body’s reaction to normally harmless substances. Allergy symptoms range from mild to life-threatening. Treatments include antihistamines, decongestants, nasal steroids, asthma medicines and immunotherapy.

What are allergies?

Allergies are your body’s reaction to a foreign protein. Usually, these proteins (allergens) are harmless. However, if you have an allergy to a particular protein, your body’s defense system (immune system) overreacts to its presence in your body.

What is an allergic reaction?

An allergic reaction is the way your body responds to an allergen.

If you have allergies, the first time you encounter a specific allergen, your body responds by creating immunoglobulin E (IgE). Your immune system makes antibodies to form IgE.

IgE antibodies bind to mast cells (allergy cells) that live in your skin, respiratory tract (airways) and the mucus membrane in the hollow organs that connect to each other from your mouth to your anus (gastrointestinal or GI tract).

The antibodies find the allergens in your body and help remove them by taking them to the mast cell (allergy cell), where they attach to a special receptor. This causes the allergy cell to release histamine. Histamine is what causes your allergy symptoms.

How common are allergies?

Allergies are very common.

More than 50 million people in the United States have an allergic reaction each year. They’re the sixth-leading cause of long-term illness in the United States.

Who do allergies affect?

Allergies can affect anyone.

You’re more likely to have or develop allergies if your biological parents have allergies.

Symptoms and Causes

What are the most common allergies?

The most common allergies include:

Certain foods

Food allergies develop when your body releases a specific antibody to a particular food. An allergic reaction occurs within minutes of eating the food, and symptoms can be severe. Symptoms may include:

  • Itching all over your body (generalized pruritus).
  • Itching in just one certain part of your body (localized pruritus).
  • Nausea and vomiting.
  • Hives.
  • Swelling around your mouth, including your throat, tongue or face.

If you have an IgE-mediated food allergy, symptoms may also include anaphylaxis. It may present as any one of the above symptoms or a combination of the above symptoms. It usually occurs within 30 minutes of ingesting a food you’re allergic to.

In adults, the most common food allergies are:

  • Milk.
  • Eggs.
  • Wheat.
  • Soy.
  • Peanuts.
  • Tree nuts.
  • Shellfish.

In children, the most common food allergies are:

  • Milk.
  • Eggs.
  • Wheat.
  • Soy.
  • Peanuts
  • Tree nuts.


Inhalant allergies are airborne substances that you inhale (breathe in). They include allergens that may affect you throughout the year (perennial allergens) and seasonal allergens.

Inhalant allergy symptoms include:

  • Runny nose.
  • Stuffy nose.
  • Itchy nose.
  • Sneezing.
  • Itchy eyes.
  • Watery eyes.

If you have asthma, inhalant allergies can also trigger or worsen your symptoms, including wheezing and shortness of breath.

Perennial allergens include:

  • Pets. Pet allergens include certain proteins in animal fur, skin (dander), urine (pee) and saliva (spit).
  • Dust mites. Dust mites are tiny, eight-legged relatives of spiders. They’re too small to see with your eyes. They live in dust and the fibers of household objects, such as pillows, mattresses, carpets and upholstery.
  • Cockroaches. Cockroaches are reddish-brown insects that are 1.5 to 2 inches (in) long. The proteins in their feces (poop), spit, eggs and dead body parts can cause allergic reactions.
  • Molds. Molds are tiny fungi (plural of fungus). They have spores that float in the air, like pollen. Common mold allergies include Aspergillus, Cladosporium and Alternaria.

Seasonal allergies include pollens. Pollen is microspores from trees, grass or weeds that appear as a fine dust on surfaces or float in the air. Tree pollens generally appear in the spring, while weed pollens generally appear in the fall.



Certain medications can cause an allergic reaction. The medicines may be herbal, over-the-counter (OTC) or prescription.

Common medications that cause allergies include:

  • Antibiotics.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs).
  • Insulin.
  • Chemotherapy drugs.

Symptoms include:

  • Rash.
  • Hives.
  • Itching.
  • Shortness of breath.
  • Swelling.
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