What Are Allergies?

An allergy is an overactive immune response to a substance (called an allergen) that is usually harmless, such as pollen or dust. Exposure to an allergy causes the body’s cells to release chemicals, such as histamines, that can cause inflammation and swelling that affects the skin, respiratory system, and digestive tract. This results in symptoms such as sneezing, itching, congestion, and rashes. In some people, allergic reactions can be life-threatening (anaphylaxis). 

There are many types of allergies, including seasonal (pollen), food, drug, pet, mold, insect, and latex allergies. Healthcare providers such as allergists and immunologists (doctors who specialize in allergic conditions) diagnose allergies through physical examination, a review of symptoms and medical history, and allergy testing. Treatment options include medications, immunotherapy, and lifestyle changes. 

Allergies are very common, affecting more than 50 million people in the United States alone. Worldwide, allergies affect up to 20% of the global population.

Types of Allergy 

There are several different types of allergies, each with specific triggers and symptoms. Understanding the different types of allergies is important for proper diagnosis and treatment.

  • Drug allergy: Drug (medicine) allergies occur when your body reacts to a specific medication.
  • Food allergy: Food allergies occur when your body views a specific food (e.g., peanuts) as harmful and causes an allergic reaction. Symptoms can include itching, hives, and difficulty breathing.
  • Pollen allergy: Also known as hay fever or allergic rhinitis, pollen allergy occurs when your body reacts to pollen from grasses, trees, and weeds.
  • Latex allergy: A latex allergy occurs when your body reacts to natural rubber latex, which is found in many products such as bandages and balloons.
  • Insect allergy: Insect allergies occur when your body reacts to the venom of stinging insects, such as bees and wasps.
  • Mold allergy: Mold (fungus) allergies occur when spores from the mold enter your airways, and your body reacts to the spores, which are found in damp or humid environments.
  • Pet allergy: Pet allergies occur when your body reacts to proteins in an animal's skin cells, urine, or saliva.
  • Other indoor allergies: Cockroach and dust mites are other common indoor allergens.

Allergy Symptoms 

Symptoms of allergies vary widely and depend on the type of allergy. Allergic reactions usually affect the area of the body that comes into contact with the allergen. For example, seasonal allergies (hay fever) occur when pollen is breathed in, so respiratory tract symptoms such as sneezing and a runny nose usually occur.

Skin Allergy Symptoms

Allergic skin reactions can occur when the skin comes into contact with an allergen (contact dermatitis). Common environmental allergens include pollen, mold, animal dander, and dust.

Common skin allergy symptoms include: 

  • Hives
  • Itching
  • Rashes
  • Swelling
  • Cracked skin
  • Redness 
  • Scaly, flaking skin

Nasal Allergy Symptoms 

Nasal allergies, also known as rhinitis or hay fever, happen when the nasal passages become inflamed after exposure to allergens. Allergic rhinitis can last for weeks or months, depending on the trigger. Common nasal allergy symptoms include:

  • Sneezing
  • Itchy nose and eyes 
  • Congestion and sinus pressure
  • Runny nose
  • Postnasal drip (mucus in the throat) 

Eye Allergy Symptoms 

Eye allergies (allergic conjunctivitis) occur when the eyes come into contact with an allergen, causing the eyes to become irritated and inflamed. Pollen, dust mites, mold spores, and pet dander can trigger eye allergies. Common eye allergy symptoms include:

  • Red, itchy eyes
  • Burning or gritty sensation in the eyes
  • Watery eyes
  • Swollen eyelids

Gastrointestinal Allergy Symptoms

Gastrointestinal allergies refer to allergic reactions that affect the digestive system. Food allergies are the most common cause of gastrointestinal allergies and can be triggered by various foods such as peanuts, tree nuts, dairy, eggs, soy, and wheat. Common gastrointestinal allergy symptoms include:

  • Abdominal pain 
  • Nausea
  • Vomiting 
  • Diarrhea
  • Cramping 


Anaphylaxis is a severe and potentially life-threatening allergic reaction that can occur quickly and without warning. It can affect multiple systems in the body, including the skin, respiratory, cardiovascular, and digestive systems. Symptoms of anaphylaxis can include:

  • Hives or skin rash 
  • Swelling of the face or tongue 
  • Difficulty breathing
  • Wheezing
  • Chest tightness 
  • Rapid or weak pulse 
  • Nausea or vomiting 
  • Pale skin 
  • Uterine cramps 
  • A sense of dread or that something bad is going to happen 

If You Have a Severe Allergic Reaction

If you are experiencing anaphylaxis, get help right away by calling 911. Anaphylaxis needs to be treated promptly with a shot of epinephrine—a hormone that’s also called adrenaline. This treatment is highly effective at slowing or stopping an allergic reaction and can be life-saving.

Even if you use epinephrine, you still need to seek immediate medical care. 


What Causes Allergies?  

Allergies occur when the body's immune system mistakenly views a normally harmless substance, such as pollen or food, as a threat and releases chemicals, including histamines, leukotrienes, and cytokines, to combat it. These chemicals can trigger the onset of allergy symptoms. 

The exact cause of allergies is not fully understood, but genetic and environmental factors are believed to play a role. People with a family history of allergies are more likely to develop allergies. Exposure to allergens when the immune system is weakened, such as during pregnancy or after an illness, may play a role in the development of allergies.

Risk Factors

Certain risk factors can raise the risk of developing allergies. Common allergy risk factors include: 

  • Family history of allergies
  • Having asthma or eczema
  • Living in an urban area
  • Age (allergies are more likely to develop during childhood/adolescence)

How Is Allergy Diagnosed?  

If you have symptoms of allergies but aren’t sure what is causing them, visit your healthcare provider. They may refer you to an allergist.

To diagnose allergies, your allergist will first ask about your symptoms, including how often you experience them and how severe they are. They will also ask about your home and work environments to identify potential allergens you are exposed to and ask about your health history and whether you have family members with allergies.

Your healthcare provider will also perform a physical examination of your eyes, ears, nose, and lungs. If you have respiratory symptoms of allergy (e.g., cough, runny nose), they may perform a lung function test to determine how well you exhale air from your lungs. 

Your allergist may recommend allergy testing to determine what allergens you are allergic to provide an accurate diagnosis. Common allergy diagnostic tests include:

  • Skin prick test: This involves exposing the skin to a small amount of an allergen. If you are allergic to a specific allergen, the exposed skin will be swollen, red, and itchy within 15 minutes. 
  • Blood test: A blood test called specific IgE (sIgE) involves taking a sample of your blood. This test measures the levels of allergen-specific antibodies to confirm an allergy.
  • Intradermal test: Similar to the skin prick test, an allergen is injected into the top layer of the skin. This test may be performed if the skin prick test is negative but your allergist suspects you have an allergy. 
  • Patch test: Commonly used to determine what allergen causes contact dermatitis, this test involves applying small patches containing an allergen onto your skin, covering it with a bandage, and examining it for an allergic reaction after 48-96 hours. A rash will develop if you are allergic to that allergen. 
  • Challenge test: A physician-supervised challenge test involves taking or inhaling a small amount of a suspected allergen in the doctor’s office (usually food or medication) to look for signs of an allergic reaction. 

In some cases, your healthcare provider may also perform additional tests, such as an X-ray of your chest and sinuses, to rule out other conditions or better evaluate the extent of your symptoms. 


There is no cure for allergies. The goal of allergy treatment is to reduce the severity of symptoms and prevent future allergic reactions. The type of treatment your healthcare provider recommends will depend on the type of allergy you have and your symptoms. 

Allergen Avoidance 

Avoiding contact with known allergens is crucial in managing allergies. Though avoiding certain allergens is difficult, taking steps to reduce your exposure can help reduce allergic reactions. Depending on your allergy, this may involve avoiding certain foods, avoiding outdoor activities or wearing a mask during peak pollen season, installing air filters in your home, and using protective clothing to avoid insect bites.


Over-the-counter and prescription medications can help control allergy symptoms. Common allergy medications include:

  • Antihistamines: These oral drugs block histamine production after exposure to an allergic to relieve symptoms such as itching, redness, hives, runny nose, and sneezing. 
  • Decongestants: These oral drugs arrow the blood vessels in the nasal passages to reduce inflammation and relieve nasal congestion.
  • Corticosteroids: These decrease inflammation and swelling to help reduce allergy symptoms. Corticosteroids may be applied topically, taken orally, or used as a nasal spray. 
  • Mast cell stabilizers: These oral or inhaled medications revent the release of histamine and other chemicals to reduce allergy symptoms. 
  • Leukotriene modifiers: These oral drugs modify the immune system's response to allergens to prevent symptoms. 
  • Epinephrine: Administered as an injection (Epi-Pen), epinephrine is used in the case of severe, life-threatening allergic reactions (anaphylaxis). 

Emergency Treatment for Anaphylaxis: Epinephrine

If you have a history of an allergy, talk to your healthcare provider about getting epinephrine auto-injectors. A common brand is EpiPen. Experts recommend carrying two epinephrine auto-injectors injections in case of an emergency. Epinephrine works by rapidly:

  • Increasing low blood pressure
  • Improving breathing
  • Decreasing swelling

If your healthcare provider has not told you otherwise, plan to go to the emergency room after using an epinephrine auto-injector that is prescribed to you. This is to ensure you receive any additional medication or care that you may need if symptoms return or worsen.


Immunotherapy involves gradually exposing small amounts of known allergens to build immunity over time. Allergen-specific immunotherapy may be recommended for people with persistent and severe allergies that are not effectively managed with other treatments or when multiple allergens are causing symptoms. 

Immunotherapy is administered in two different ways: subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT).

Subcutaneous Immunotherapy (SCIT)

Known as allergy shots, SCIT is injections given 1-2 times per week for about six months until a maintenance dose is reached. After that, the maintenance dose is usually continued at least once a month for three to five years. Each injection contains a small amount of the allergen(s) when the therapy begins. Over time, the dose gradually increases to reduce sensitivity to the allergen and shots are given less frequently. People usually notice improvement by the time they reach maintenance doses.

Sublingual Immunotherapy (SLIT)

With SLIT, small doses of an allergen are given under the tongue to make the immune system less sensitive to the allergen and reduce symptoms. It may take up to 14 weeks of SLIT to notice a difference in symptoms. 

How to Prevent Allergy Attacks

Preventing an allergic reaction isn’t always possible, but preventive measures can help reduce the frequency and severity of allergic reactions. Here are some ways to avoid allergy attacks:

  • Identify and avoid allergens: Understanding what triggers your allergies is the first step in avoiding them. Allergy testing and tracking your symptoms will help you identify which allergens to avoid and when to take extra precautions (e.g., during pollen season). 
  • Reduce indoor allergens: Keep windows closed, use allergy-proof bedding, install air filters, and vacuum regularly to reduce allergens in the home.
  • Take allergy medications: Follow your healthcare provider’s treatment recommendations and take your medications as prescribed to help control symptoms.

Your healthcare provider can work with you to determine the best approach for preventing allergy attacks and managing symptoms when they do occur. 

Comorbid Conditions

Allergies are often associated with other medical conditions, which can occur together (comorbidity). Some of the most common comorbid conditions associated with allergies include:

  • Asthma: Asthma is a chronic lung disease that causes the airways to be inflamed and narrow, making breathing difficult. 
  • Eczema (atopic dermatitis): Eczema is a skin condition characterized by itchy, red, and dry skin. 
  • Sinusitis: Sinusitis is an inflammation of the sinuses that can cause headaches, facial pain, and nasal congestion. 
  • Gastrointestinal disorders: People with allergies are more likely to develop gastrointestinal conditions like eosinophilic esophagitis (EoE).
  • Mental health conditions: Living with allergies can impact your mental health, and research shows that people with allergic conditions have an increased risk of depression and anxiety

Living With Allergies  

Living with allergies isn’t easy. Experiencing symptoms and taking extra steps to avoid allergens can take a toll on your physical and mental health. The good news is proper management of allergies can help reduce the impact allergies have on your daily activities and improve your quality of life. Learning about your allergy, avoiding allergens, and following your treatment plan can help you live well. 

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Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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