Allergies

People can mistake allergy symptoms for colds, stomach bugs, and common rashes.

While common allergies are often mild, some can be serious.

If you think you have an allergy, you should see a doctor. They can test you to find out what's causing your allergic reaction and suggest a treatment.

Looking for Allergy Care?

On this page

• What Are Allergies?
• What Are the Symptoms of Allergies?
• How Do You Diagnose Allergies?
• How Do You Treat Allergies?

What Are Allergies?

Allergies are an immune system reaction to a substance in the environment.

In an allergy, the immune system mistakes a chemical in food, the air, or an insect, as if it's harmful. Allergy symptoms like sneezing, swelling, and vomiting are the body's attempts to flush out the allergen.

Around a third of people in the U.S. have allergies each year. Pollen allergies are the most common.

What are the types of allergies?

There are many types of allergies.

They include:

• Drug allergy. An allergy to a medicine.
• Food allergy. An allergy to one or more foods.
• Hay fever. An allergy to pollen in the air.
• Insect allergy. A reaction to a stinging insect, like a bee or mosquito.
• Latex allergy. Latex in gloves or condoms cause skin symptoms and can even cause anaphylaxis.
• Mold allergy. A reaction to mold spores in the air.
• Pet allergy. A reaction to the dander of dogs, cats, or other pets.
• Skin allergy. Involves a rash like hives, contact dermatitis, or eczema.

What causes allergies?

An allergic reaction happens when the immune system makes antibodies to target a foreign substance.

It's not clear why the immune system overreacts.

With food allergies, research shows that a lack of exposure early in life can lead to an allergy later. For instance, parents can introduce peanuts at around 6 months of age.

What are allergy risk factors and complications?

Allergy risk factors

• Age. Allergies are more common in children. However, adults can get an allergy to things they were able to tolerate well in the past.
• Existing allergies. People with one type of allergy — like eczema — are more likely to get another type, like a food allergy.
• Family history. People with a parent or sibling with an allergy are more likely to have an allergy.

Complications of allergies

Sometimes, allergens can cause anaphylaxis — a life-threatening allergic reaction that leads to very low blood pressure and trouble breathing.

Symptoms often occur throughout the body and come on within minutes to an hour of exposure.

In rare cases, anaphylaxis can lead to organ damage and even death.

People with an anaphylactic reaction need treatment right away.

Back to top

---

Allergy Symptoms and Diagnosis

What are the signs and symptoms of allergies?

Allergy symptoms can include one or more of the following:

• Itchy eyes.
• Watery eyes.
• Runny nose.
• Swelling of the face, or part of the face, like the eyes or lips.
• Sneezing.
• Coughing.
• Itchy skin.
• A rash.
• Stomach pain.
• Trouble breathing or swallowing.
• Vomiting or diarrhea.

The symptoms depend on how severe your allergy is and how you came into contact with the allergen.

For instance, if you breathe in the allergen, you may have symptoms in your nose, eyes, and mouth. If you eat the allergen, you may vomit or have diarrhea.

If someone shows signs of anaphylaxis, they need to see a doctor right away.

Signs of anaphylaxis include:

• A rapid drop in blood pressure.
• A fast heartbeat.
• Anxiety.
• Blue lips.
• Clammy skin.
• Confusion.
• Trouble breathing.

How do you diagnose allergies?

Your doctor will first ask about your symptoms, including what happened and how long the symptoms lasted.

They will also ask questions to figure out what the allergen was, such as:

• Did your symptoms occur after eating a food you don't eat often?
• Have you had a reaction like this before?
• Do your symptoms happen when you spend time outside or inside?
• Have you started using a new product on your skin or in your home?

Your doctor will also ask about how you treated your symptoms. If an over-the-counter anti-allergy treatment helped, an allergy is likely.

There are tests for allergies, but these tests aren't always 100% certain.

Your doctor may need to try more than one test. They may combine tests with your symptom history to make a diagnosis.

Skin test to diagnose allergies

The nurse or doctor will:

• Put a small drop that contains the possible allergen on your skin.
• Prick your skin so that the allergen can go past the outer layer.
• Check the reaction after 15 minutes.

If you're allergic, the area will become red, swollen, and itchy.

Skin tests can diagnose common allergies, including to certain types of pollen, dust mites, and foods.

But skin tests aren't always accurate, especially when it comes to food. The skin may react even though the allergen wouldn't cause a problem if eaten.

Blood test to diagnose allergies

Blood tests may be better than skin tests for people who:

• Are taking medicines that could affect the skin test results.
• Have skin issues.
• May have a serious reaction to a skin test.

In a blood test, the doctor takes a small amount of blood and sends it to the lab. There, a lab tech adds the suspected allergen to the blood.

If your blood cells produce a high level of antibodies in response, you likely have an allergy.

Patch test

This test checks for allergic reactions that happen from contact with the skin (unlike allergens you breathe in or ingest).

The doctor will place a bandage-like patch on the skin with a small amount of the allergen. They'll check under the patch after 2 or more days for allergy symptoms.

Oral challenge test to diagnose allergies

Your doctor may suggest an oral challenge test for a food or drug allergy. They won't choose this test if a serious reaction is likely.

In an oral challenge test, you consume a very small amount of the allergen in a health care clinic. The care team checks for signs of a reaction.

They can treat any serious reaction right away.

Back to top

---

What Are the Treatment Options for Allergies?

Doctors treat allergies with medicines in pill, inhaler, nasal spray, injection, or cream form.

These treatments can:

• Relieve allergy symptoms for a short time.
• Stop anaphylaxis.
• Prevent allergic reactions from occurring.

Antihistamines to treat allergies

This is the most common allergy medicine, and you don't need a prescription.

Antihistamines block histamine, the chemical released in allergic reactions.

This oral or nasal spray medicine can treat mild to moderate allergy symptoms.

Many antihistamines cause you to become drowsy. If you need to stay awake to drive or work, look for a "non-drowsy" formula.

Corticosteroids for allergies

These medicines reduce the activity of the immune system.

Your doctor may suggest an oral or a cream corticosteroid based on your type of allergy.

Decongestants

These over-the-counter drugs reduce swelling in the nose.

They can bring short-term relief to a runny nose or watery eyes.

Mast cell stabilizers

These medicines stop the body from releasing antihistamines. You need to take them before exposure to an allergen for them to work.

Epinephrine to treat allergies

This treatment reduces or stops anaphylaxis. It relaxes muscles to stop swelling in the airways and tightens blood vessels to raise blood pressure.

Anyone at risk of anaphylaxis should carry epinephrine with them at all times.

Immunotherapy for allergies

With this treatment, people get a shot or an oral form of a tiny amount of their allergen. The amount increases slowly over time so that the immune system gets used to it and doesn't react.

This can help cure certain allergies, such as:

• Pollen.
• Pet dander.
• Dust mites.
• Some insect bites.

Researchers are seeing if this can work for certain food allergies, like peanuts.

Back to top

---

By UPMC Editorial Staff. Last reviewed on 2024-03-28.