What Are Allergies? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Allergies occur when your immune system overreacts to substances called allergens. Common allergens that can trigger allergic reactions include pollen, pet dander, and bee venom. People also have allergies to certain foods and medications.

Signs and Symptoms of Allergies

Allergy symptoms vary depending on the type of allergens.

Allergic rhinitis (commonly known as hay fever), for instance, is associated with the following symptoms:

  • Sneezing
  • Runny nose
  • Congestion
  • Itchy eyes, nose, and throat
  • Tearing eyes

An allergic food reaction may share some of the above symptoms, but it can also cause:

  • Diarrhea, nausea, and vomiting
  • Hives, eczema, or itchy skin
  • Anaphylaxis, in which a narrowing of the airways makes it difficult or even impossible to breathe

A skin allergy or insect bite can cause the following at the site:

  • Redness
  • Swelling
  • Hives
  • Pain
  • Itching

The symptoms of a drug allergy may include:

  • Hives
  • Wheezing
  • Light-headedness
  • Vomiting
  • Swelling of the face or throat

Learn More About Signs and Symptoms of Allergies

Causes and Risk Factors of Allergies

Your risk of developing allergies is higher if you:

  • Have asthma
  • Have a family history of asthma or allergies
  • Are younger than 18

Children sometimes outgrow allergies as they get older. It's also not uncommon for allergies to go away and then return years later.

You may have more than one allergy. Children with food allergies, for instance, are as much as four times more likely to have other allergic conditions, including asthma.

More than 100 genes are associated with allergies, although only one or two genes affect any given population. Some of these genes affect the immune response; others affect lung and airway function.

Allergic Reactions

Allergens are typically harmless substances that trigger an immune response and cause a reaction in people who are allergic. The allergic reaction occurs if the person inhales, touches, swallows, injects, or somehow comes into contact with the allergen. Allergic reactions can be mild, severe, or even life-threatening.

Normally, the immune system protects the body against harmful substances, such as viruses or bacteria. If you have allergies, "your body responds to allergens as if they were invaders," explains Clifford Bassett, MD, a clinical assistant professor at New York University Langone Health in New York City and the author of The New Allergy Solution. "Your body exaggerates the immune response. That's what causes histamine release and other things that cause allergy misery."

Histamine also acts as a neurotransmitter in the brain, sending messages between cells. It plays a key role in many different physiological functions, such as telling your stomach to produce acid to digest food or helping regulate your sleep-wake cycle.

When your immune system reacts to an allergen, it produces an antibody called immunoglobulin E (IgE). The production of IgE is part of your body's attempt to destroy the allergen and protect itself. Your blood vessels dilate and become leaky, so white blood cells that fight infection and other protective substances leave the blood vessels to attack the invader.

In the process, the IgE antibodies signal other cells to release certain chemicals, such as histamine in the local tissue and blood stream. Too much histamine or excessive release in the body can cause an unwanted response that leads to skin, nose, throat, and lung irritation or more severe symptoms of anaphylaxis.

In this way, a normally protective process creates a cascade of what we know as allergy symptoms in response to harmless allergens.

There are other types of allergic reactions, such as delayed hypersensitivity reactions, which includes contact dermatitis from poison ivy or a nickel allergy — these are mediated by T cells in the immune system rather than antibodies.

The most common allergens that trigger allergic reactions include:

  • Pollen
  • Dust mites
  • Pet dander or fur
  • Cockroaches
  • Mold spores
  • Foods (eggs, fish, milk, nuts, wheat, soy, shellfish, and others)
  • Insect stings or bites (from wasps, bees, mosquitoes, fire ants, fleas, horseflies, black flies, among others)
  • Medicines (penicillin, aspirin, and others)
  • Latex
  • Household chemicals
  • Metals (especially nickel, cobalt, and chromates)

Seasonal Allergies

Certain allergies can strike at any time of year. Seasonal allergies, on the other hand, occur at times of the year when certain types of outdoor allergens are predominant.

"You can have both," says Dr. Bassett.

And about two-thirds of people with seasonal allergies actually have year-round or persistent allergies, according to the American College of Allergy, Asthma & Immunology.

Seasonal allergies are most often triggered by mold and pollen from trees, grasses, and weeds such as ragweed. The allergic reaction occurs during the weeks or months when the plant pollinates.

Allergy triggers may vary depending on geographic location and climate, but relocating to avoid seasonal allergies generally doesn't help. Pollen and mold spores travel great distances; and people with allergies often develop sensitivity to other allergens in a different location.

Environmental factors such as pollution and climate change associated with rising temperatures may be contributing to a rise in allergies. Changes in the duration and intensity of pollen and mold seasons mean more people are exposed to allergens for longer amounts of time. "That's a longer period of time for your eyes and nose and throat to become symptomatic as a result," Bassett says.

In a 2015 survey of allergists, 63 percent of respondents felt climate change was causing an increase in allergic symptoms among their patients.

How Are Allergies Diagnosed?

The first step in diagnosing allergies is an evaluation by your physician to review your symptoms and medical history and to rule out other potential medical problems. You can help your doctor make an accurate diagnosis by keeping a record of your symptoms, including when they started and what triggers them.

If allergies are suspected, your doctor may order tests. These include skin and blood tests. Your doctor may also perform a lung function test or an X-ray of your lungs.

Is It an Allergy or Something Else?

Like allergies, a cold and the flu affect the respiratory system; and they share some symptoms, such as a runny nose and coughing.

One difference between them is the itchiness associated with many allergic reactions.

"Typically, an allergy will have itchiness of the eyes, nose, and throat," says Bassett. "With a cold, you're more likely to have a sore throat, decrease in appetite, and you just don't feel well."

Allergy symptoms last as long as you are exposed to an allergen, whereas a cold or the flu usually runs its course within two weeks. Flu symptoms tend to be more severe than cold symptoms, accompanied by a fever and possibly headache, fatigue, and aches and pains.


Allergies or COVID-19? Here’s How to Tell the Difference

"If you have a cold, there's no real good treatment other than waiting five to seven days," Bassett says. But for a nonsevere allergy, "if you use an antihistamine or nasal steroid spray, they're usually very effective."

The coughing and other respiratory symptoms of COVID-19, the infection caused by the SARS-CoV-2 coronavirus, may also be confused with allergies. One notable difference is that fever, which often accompanies COVID-19 and the flu, isn't usually a sign of allergies. Another difference: Allergic coughing is typically the result of postnasal drip, unlike the dry COVID-19 cough.

Other conditions that produce allergy-like symptoms include:

  • Non-allergic rhinitis, which mimics allergic rhinitis but does not involve the immune system (at least one-third of people with rhinitis symptoms don't have allergies)

  • Sinus infections
  • Nasal polyps or a deviated septum

Prognosis of Allergies

There are different prognoses for different types of allergies.

Rhinitis Typically, allergic rhinitis peaks in adolescence and gradually improves as people get older. A study published in Allergy Asthma Proceedings followed college freshmen with hay fever and found that at the end of the 23-year follow-up, 54.9 percent of the subjects showed improvement in symptoms, with 41.6 percent of those being symptom-free. Investigators concluded that over a long period of time, hay fever symptoms will improve in the majority of people.

Asthma According to the CDC, 3,524 people died in 2019 from asthma in the United States. Many asthma deaths are avoidable; most people can maintain a normal, healthy life with asthma provided they work with their doctor to make sure they are avoiding triggers and taking their medications properly.

Food allergies The prognosis depends on the type of food allergy. Most infants and children outgrow allergies to milk, eggs, soy, and wheat. Peanut, tree nut, fish and shellfish allergies are more persistent and can last a person's whole life in some cases.

Skin allergies A skin rash and contact dermatitis that appears as a reaction to something irritating the skin usually clears up within a few weeks. If it doesn't, a healthcare professional should be consulted.

About 50 percent of children with eczema will outgrow the condition or have significant improvement by the time they reach puberty. Most adults who have eczema can manage the disease with good skin care and medical treatment, but flare-ups may happen periodically throughout their lifetime.

Duration of Allergies

Some allergies last for a number of years and then go into remission, and others can last a lifetime, says John Bosso, MD, the director of the otorhinolaryngology allergy clinic at Penn Medicine in Philadelphia.

"For example, a certain percentage of people with asthma and allergic rhinitis can get better with time — often it improves in puberty, especially in boys," says Dr. Bosso.

There are cases where allergies go away, even if someone has had them a good part of their lives. "A person in their forties or fifties may find that they no longer react to things in the environment," he says.

The reverse can happen as well — someone without a history of allergies can develop them in adulthood. This can be triggered by moving to a new geographic region or for other reasons that aren't completely understood.

"Many food allergies are transient; they can last for a few years and then go away," says Bosso. "Milk and egg allergies are frequently outgrown, but not always. Tree nut allergies are permanent in the majority of people — about 80 percent have it long-term," he says.

Treatment and Medication Options for Allergies

There are no cures for allergies, but effective treatment can reduce symptoms and improve your quality of life.

Allergy treatments vary, depending on the severity of your condition and the type of allergy you have.

Medication Options

If your allergies are severe enough to significantly interfere with your quality of life, it's a good idea to see a doctor in order to identify what you're allergic to and to gain access to the full range of prescription options.

If your allergies are less severe or merely annoying, you may be able to find an effective over-the-counter (OTC) treatment. A pharmacist may be able to help you choose the best option based on your symptoms.

OTC medicines include antihistamines and decongestants and nasal steroid sprays (which relieve congestion and previously were prescription). Cromolyn is a nasal spray used to help prevent or treat allergy symptoms, and there is also montelukast (Singulair) that is used for asthma and allergic rhinitis.

Your doctor may prescribe allergy shots (immunotherapy), which lessen your immune system's reaction to allergens, and steroids, which reduce inflammation and swelling.

You may also need medications for asthma. If you have severe allergic reactions and are at risk for anaphylaxis, then your doctor may recommend that you carry a dose of epinephrine, a chemical that narrows blood vessels and opens airways in the lungs.

In 2020, the U.S. Food and Drug Administration (FDA) approved Palforzia (peanut allergen extract), a medication help reduce the severity of allergic reactions to peanuts, including anaphylaxis, in children age 4 through 17.

Alternative and Complementary Therapies

Complementary remedies, such as acupuncture, and nasal irrigation techniques may also help relieve allergy symptoms.

A study published in June 2018 in Acupuncture Medicine found that patients receiving acupuncture needed less medication and had fewer symptoms of seasonal allergic rhinitis than the control group.

A number of other complementary and integrative medicine approaches for asthma, eczema, and other allergic symptoms have a variety of supporting evidence. These include breathing exercises, dietary changes, and herbal remedies.

Bosso cautions people about using alternative therapies to treat allergies. "Many things that purport to treat allergies are available because in the supplement/non-pharmaceutical market you don't need to prove efficacy or that it's better than placebo, it just needs to be proven to be safe," he says.

It's often best to discuss with your primary care provider or another healthcare practitioner who is knowledgeable about integrative and complementary medicine and can help you determine if some of these therapies may support your treatment goals safely.

Learn More About Treatment for Allergies: Medication, Alternative and Complementary Therapies, and More

Prevention of Allergies

There are some measures you can take to prevent or limit allergic reactions at home. The following have varying degrees of supporting research but are generally safe and low cost:

  • If you're allergic to pollen and you know pollen counts are going to be high, try to remain inside with doors and windows closed. The National Allergy Bureau provides pollen and mold updates by region.
  • Use a high-efficiency particulate air filter (HEPA). HEPA filters trap airborne allergens.
  • If you already have a cat or dog that you're allergic to, don't sleep near the pet, and wash your hands promptly after contact. Don't touch your eyes, nose, or mouth after touching an animal.
  • If you're trying to figure out which allergens might cause or worsen your symptoms, keep a log. Write down what you eat and all your activities to help pinpoint triggers.
  • Wash bedding frequently and use hot water to lessen your exposure to dust mites, pet dander, pollen, and other airborne irritants.
  • If you have severe allergies, a medical alert bracelet or necklace can aid in getting you medical assistance in an emergency.

Complications of Allergies

People with allergies are at risk of developing complications that range from mild to potentially life-threatening.


One of the most serious allergic complications is anaphylaxis, which is commonly associated with allergies involving food, drugs like penicillin, and insect venom.

Symptoms of anaphylaxis may include:

  • A drop in blood pressure
  • Loss of consciousness
  • Severe shortness of breath
  • Skin rash
  • Rapid or weak pulse
  • Nausea or vomiting
  • Light-headedness
  • Severe wheezing
Anaphylaxis is a medical emergency. It can cause seizures, arrhythmia (irregular heartbeat), shock, or respiratory distress.

If you or someone around you has an anaphylactic reaction, call 911 or seek immediate medical attention.


Asthma is a chronic lung disease characterized by inflamed airways and trouble breathing. An asthma attack causes chest tightness, coughing, wheezing, and episodes of severe shortness of breath.


What Type of Asthma Do I Have?

More than 24 million people in the United States have asthma, according to the Centers for Disease Control and Prevention (CDC).

Allergies and asthma are on a spectrum and frequently overlap, says Bassett. Ninety percent of children and 50 percent of adults with asthma have allergic asthma.

Allergic asthma causes inflamed airways to become irritated and over-respond when an irritant is inhaled, triggering an asthma attack. The muscles around the airways tighten, making the airways swell and overproduce mucus. The risk of developing asthma if you have allergic rhinitis is significant, Bassett says.

Other Allergic Complications

People with allergies are also at risk of developing:

  • Eczema (a skin condition characterized by inflammation)
  • Ear or lung infections
  • Sinusitis or sinus infection
  • Nasal polyps (growths on the lining of the nose or sinuses)

  • Migraine headaches

Research and Statistics: How Many People Have Allergies?

Allergies are the sixth leading cause of chronic illness in the United States. More than 50 million Americans each year suffer from an allergy-related disease or condition.

According to the CDC, at least 19 million Americans 18 and older and more than 5 million children were diagnosed with allergic rhinitis (hay fever), in 2018. Another 21 million American children were diagnosed with respiratory, food, or skin allergies.

Black and Hispanic Americans and Allergies

Black Americans and Hispanics are disproportionately impacted by allergies and asthma and tend to have more serious cases, says Bosso.  

Black and Hispanic Americans and Allergies

Black Americans and Hispanics of Puerto Rican origin have the highest rates of asthma in the United States, as well as the highest number of emergency room visits and hospital stays due to asthma. Black Americans and Puerto Ricans are three times more likely to die due to asthma than white Americans.

Minorities are less likely to be included in clinical trials that test the efficacy and safety of drugs, and this can lead to disparities in treatment.

This seems to be especially important in asthma, as there is evidence that in some instances Black and white populations may respond differently to certain medications, as suggested in a study published in the New England Journal of Medicine.

Black and Hispanic Americans are also at a higher risk for exposure to air pollution, which contributes to worsening of allergies and asthma. The American Lung Association, citing 2019 data from the Environmental Protection Agency, notes that nonwhite populations, especially Black Americans, faced higher risk from particle pollution.

Related Conditions and Causes of Allergies


Also called atopic dermatitis, this condition makes skin red and itchy. It's most often found in children, but adults can have eczema, too. More than half of children with eczema also have asthma and hay fever by the time they reach puberty.

Obstructive Sleep Apnea (OSA)

People with allergic rhinitis can often have sleep problems, including insomnia, restlessness, and obstructive sleep apnea. And there seems to be a correlation between the severity of someone's allergies the severity of their sleep problems.

Research also suggests that allergic rhinitis is a risk factor for OSA in children.

RELATED: What Is Eosinophilic Esophagitis (EoE)? Symptoms, Causes, Diagnosis, and Treatment

Resources We Love

American Academy of Allergy Asthma & Immunology (AAAAI)

The AAAAI is a professional association of immunologists, asthma specialists, and allergists. The organization offers educational resources, a symptom test to determine if you suffer from allergies or asthma, and a tool to help you locate a specialist in your area.

Asthma and Allergy Foundation of America (AAFA)

This not-for-profit organization is dedicated to saving lives and reducing the burden of asthma and allergies through support, advocacy, education, and research. It also has local chapters and support groups throughout the country.

Food Allergy Research & Education (FARE)

FARE’s mission is to improve quality of life and health for Americans with food allergies. The group advocates for research and provides resources and support for people in the food allergy community.

Additional reporting by Becky Upham.

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