What is an allergic reaction?

Almost one in three U.S. adults and one in four U.S. children have a seasonal allergy, eczema or food allergy. Common allergens include not only pollen and food but also insect stings, latex and medication and latex. And while some allergic reactions cause only mild symptoms, others can be life-threatening.

Learn how to recognize an allergic reaction, what to do in case of anaphylaxis and how a health care provider determines what someone is allergic to.

In this article:

Why allergic reactions occur

While allergies tend to be more common in children, they can affect people of any age, gender and race. An allergic reaction happens when the immune system overreacts to an allergen (a substance that the system decides is harmful). This can happen when someone absorbs, inhales,\ or ingests allergens into their body.

Understanding the immune system

The immune system’s job is to protect the body from disease-inducing bacteria, fungi and viruses. If any infectious microorganisms do enter the body, the immune system will destroy them to shield the body from infection.

Allergens trigger an immune response because the immune system thinks it needs to protect the body from substances it’s allergic to (like dust or pollen). The immune system responds by producing antibodies, which then results in symptoms like itching, a runny nose or wheezing.

What’s more, most allergic reactions are “hypersensitivity” reactions. These can either be immediate (occurring within minutes to hours of allergen exposure) or delayed (happening within a day or two of exposure to the allergen). Delayed hypersensitivity reactions are typically milder.

Common allergic reactions

Allergens that can provoke the immune system range from things like fish or peanuts to mold or smoke.

Food allergies

In the U.S., 5.8 percent of children and 6.2% of adults have a food allergy. Food allergies can cause traditional allergic reaction symptoms, such as hives and trouble breathing; lip, throat and tongue swelling; or gut-related symptoms like diarrhea and vomiting.

Most food allergies are caused by the following:

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

Inhalants

Inhalant allergies, or airborne allergens that enter the body via someone breathing them in, cause symptoms like coughing, a headache, itching, an itchy throat, red eyes, a runny nose, sneezing, trouble smelling or watery eyes. Common inhaled allergens include the following:

• Animal dander
• Cockroach saliva or excrement
• Dust mites
• Feather (down or eiderdown)
• Mold
• Pests (mice or rats)
• Pollens (grass, trees or weeds)

Fragrances, household chemicals and smoke do not technically cause allergies. They cause irritant reactions, which can masquerade as allergies.

Insect stings and venom

The most common insect stings are from fire ants, honeybees, hornets, wasps and yellow jackets. While many people experience more minor symptoms, such as flushing, hives, itching, pain, redness and swelling, others may go into anaphylaxis, a severe reaction that may be life threatening.

Latex

Natural rubber latex is a fluid that comes from the sap of the rubber tree. It’s used as an ingredient in many products:

• Airway and intravenous tubing
• Athletic shoes
• Baby bottles
• Balloons
• Bandages
• Catheters
• Condoms
• Dental dams
• Disposable gloves
• Dressings
• Handbags
• Nipples
• Pacifiers
• Rubber toys
• Stethoscopes
• Syringes
• Tires
• Tools
• Underwear

If someone is allergic to latex, direct contact with latex can cause an allergic reaction, potentially resulting in symptoms like chest tightness, hives, itching, redness or a runny nose.

Medications

Some people are allergic to prescription drugs and medications. Common medications that cause allergies can include the following:

• Antibiotics containing sulfonamides
• Antibiotics similar to penicillin
• Anticonvulsants
• Chemotherapy drugs
• Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and ibuprofen

People who are allergic to these medications can still have symptoms whether the medication is taken as a liquid, pill or injection. Symptoms of an allergic reaction to medication can present as anaphylaxis, hives, itching, swelling or wheezing.

Symptoms of allergic reactions

Depending on the severity of someone’s allergies, their symptoms during an allergic reaction can either be mild or severe.

Mild symptoms

Symptoms of a mild allergic reaction to inhalant or airborne allergies often include a runny nose, sneezing, a sore throat and allergy-induced red eyes. For mild food allergies, short-lived abdominal cramps, diarrhea and vomiting as well as lip, throat and tongue swelling are common. For contact allergies and insect stings, hives or a rash around the site of the sting, itching, redness and swelling are the most likely symptoms.

Severe symptoms (anaphylaxis)

Anaphylaxis is a serious allergic reaction that needs immediate medical attention: an injection of epinephrine and a visit to the emergency room. Anaphylaxis can be life threatening.

People who have allergies, asthma or a family history of anaphylaxis or who have had anaphylaxis in the past are at a greater risk of having an anaphylactic reaction. Warning signs of anaphylaxis include the following:

• Diarrhea
• A feeling of impending doom
• A hoarse voice
• Itchy red rash with hives
• Loss of consciousness
• A pale or red color in the face and on the body
• Stomach cramping
• A swollen throat
• Tightness in the chest
• Trouble breathing and swallowing
• Vomiting
• Wheezing

Diagnosis of allergic reactions

If someone believes they are experiencing allergic reactions, they should let their primary health care provider know. They will likely refer their patient to an allergist, a health care provider who specializes in treating allergies.

Blood test

Bloodwork is another method of diagnosing allergies. A health care provider will rely on their patient’s test results along with the rest of their medical history to help them figure out what they are allergic to.

Identifying triggers

If someone has food allergies, identifying the foods that trigger their symptoms is important in making a diagnosis. However, this needs to be done in a safe environment in case someone has a severe allergic reaction.

Skin test

Allergists commonly use skin testing to determine what allergies someone has. A prick or scratch test puts a tiny drop of an allergen into the skin to see how the body reacts. An intradermal test injects the allergen under the skin. Both tests can be quickly completed in the health care provider’s office.

Treatment and management of allergic reactions

Having an allergic reaction can be a scary experience. If someone lives with allergies, however, there are steps they can take to manage their allergies and hopefully reduce the number of allergic reactions that they have.

Allergy immunotherapy

Some people can receive allergy desensitization shots on a regular basis to help control their symptoms and reactions. These shots are a form of immunotherapy. They introduce small doses of an allergen to help the immune system become less sensitive to it.

Immunotherapy is the only Food and Drug Administration (FDA) approved method of allergy desensitization. It’s often used for airborne or inhalant or airborne but can also be used for certain severe stinging insect allergies or peanut allergies.

Anaphylaxis treatment

If someone is having an anaphylactic reaction, they should be administered a shot from their epinephrine device using the instructions on the injector and 911 should be immediately called. While an ambulance is on the way, the person affected should lie down and not stand up or walk. If symptoms are not improving after 15 minutes, they should be administered another shot of the epinephrine, if available.

Medications

There are several types of allergy medicine and OTC allergy treatments that can help the symptoms of an allergic reaction subside:

• Antihistamines
• Corticosteroid creams or ointments
• Decongestants
• Epinephrine injection
• Injectable prescription medications
• Mast cell stabilizers
• Nasal corticosteroids
• Oral prescription medications
• Saline nasal spray

Preventing allergic reactions

If someone in the household has allergies, actions can be taken to minimize triggers and avoid allergic reactions. For food allergies, thoroughly read ingredient labels and packaging. If someone travels or eats at a restaurant, they should communicate with the waitstaff or chef about their needs.

For inhalant allergies, clean the home regularly (particularly in tiled areas) so mold does not grow. Don’t allow smoking inside the house. For a heating, ventilation and cooling (HVAC) system, it’s best to use a disposable air filter with a minimum efficiency reporting value (MERV) rating of 11 to 13 to catch dust mite allergens, pollen and pet allergens.

Finally, people with allergies should create an allergy action plan. Anyone with allergies as well as their family members and close friends should know how to use an epinephrine pen and what to do in case of an anaphylactic reaction.

When to seek medical help

People should see an allergist if their allergies are affecting their day-to-day life and their symptoms cannot be controlled with over-the-counter medications. Another reason to see an allergist is if someone experiences hay fever several months out of the year or their allergies are causing symptoms like chronic sinus infections. Finally, it’s important for someone to see an allergist if they have suspected drug, food or insect sting allergies or chronic urticaria (which causes frequent hives and swelling).

Dealing with allergic reactions

Allergic reactions need proper, prompt treatment to keep the affected person safe. Knowing triggers and having an allergy action plan are the recommended ways to deal with allergic reactions when they arise.

Frequently asked questions

What defines an allergic reaction?

An allergic reaction happens when the immune system overreacts to an otherwise harmless substance (like food, pet dander or pollen). This reaction causes symptoms like difficulty breathing, itching and swelling.

What are some possible symptoms of an allergic reaction?

Possible common symptoms of an allergic reaction are breathlessness; diarrhea; facial pain; feeling faint or lightheaded; hives; a rash; a runny nose; swelling in the face or throat; and wheezing.

What is the difference between a cold and allergies?

A cold is caused by a virus. Allergies are caused by the body’s immune system reacting to an allergen (such as dust mites or pollen).

How long can allergies last?

Symptoms caused by allergies can persist for as long as someone is exposed to the allergen. Seasonal allergies (for example, pollen) may only last for a few weeks. Other allergies might cause symptoms for the entire year. Dust mites, feathers, mold, pet dander, and rodent or cockroach infestations can cause perennial symptoms that last for months or years.

Can children outgrow allergies?

Yes. In some cases, children might outgrow certain allergies as their immune system develops.

This content is for informational purposes only and is not medical advice. Consult your health care provider before taking any vitamins or supplements and prior to beginning or changing any health care practices.