What Is an Allergen?

Reviewed by: HU Medical Review Board | Last reviewed: March 2022

Allergens are substances that trigger allergy symptoms for children and adults. Literally anything can be an allergen. Allergens that cause a reaction for 1 person may not affect other people. Common allergens include:1-7

  • Pet dander
  • Pollen (grass, trees, weeds)
  • Dust mites
  • Insects
  • Rodents
  • Food
  • Drugs
  • Mold

It is important to know which allergens trigger your symptoms. Avoiding exposure to your allergens may reduce your symptoms and keep you more comfortable. This can help reduce the amount of allergy drugs you need to take. Avoidance can also keep you safe and prevent you from having a severe allergic reaction.1-7

Avoiding your allergens can also help reduce asthma attacks in people who have allergic asthma. This is asthma triggered by allergens.1

About allergens

An allergic reaction happens when your body thinks a foreign substance is a threat. Allergens can enter the body by breathing, swallowing, or touch. After exposure to an allergen, your immune system recognizes it as foreign and tries to fight off the danger. Your immune system tries to protect you by releasing a chemical called immunoglobulin E (IgE).1

High amounts of IgE can trigger inflammation by activating special allergy cells called mast cells. This can lead to sneezing, runny or stuffy nose, hives, itchy nose, eyes, mouth, and throat. More severe allergic reactions can lead to increased swelling of the airways, making it hard for you to breathe.1,2

Common allergic reactions

The type of symptoms you have during an allergic reaction depends on many factors, including the allergen you are reacting to and how much of the allergen you are exposed to. Reactions can be mild, moderate, or severe. You may have mild reactions for years and suddenly have a severe reaction, or vice versa. The most common allergens are:2

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  • Airborne substances such as pollen, pet dander, dust mites, and mold
  • Foods like peanuts, tree nuts, wheat, soy, fish, shellfish, eggs, and milk
  • Insect stings from bees, wasps, and yellow jackets
  • Drugs like certain antibiotics or aspirin
  • Natural rubber latex

Pet dander

Dander refers to flakes of dried skin, glands, and saliva from animals with fur. Dander from cats and dogs trigger allergies for many people. Between 25 and 50 percent of children with asthma are sensitive to pet dander.3

Pet dander is even found in homes and schools with no pets. Pet dander allergens remain in the air for some time before settling down. This means they can be carried by people to places without a pet.3

Ways to reduce the impact of pet dander on your allergies include:3,4

  • Keeping pets out of your bedroom
  • Grooming and bathing them often
  • Using a vacuum and air cleaner with a HEPA filter
  • Using allergen-proof bedding
  • Feeding cats special food that reduces their allergen

If dander is still triggering your allergies, you may want to find the pet another home. It may take several months for allergens to go away after removing a pet.

Talk to your vet about finding them a new home. Also ask them about myths about pet dander allergies. For example, “non-allergenic/hypo-allergenic” or short-hair pets may not reduce your sensitivity. This is because the allergen mostly comes from their skin and saliva, not their hair.3

Dust mites

Dust mites are tiny pests that live on soft surfaces, such as carpets, bedding, pillows, drapes, and upholstered furniture. The mites and their feces can be allergens. Dust mites live on skin flakes and need moisture to grow.3-5

It is also hard to completely avoid dust mites unless you live in a very dry climate. There are ways to reduce your exposure, such as:3-5

  • Use dust-proof bedding
  • Wash your bedding weekly in hot water and dry completely
  • Vacuum carpets and rugs often
  • Remove carpets and drapes from bedrooms
  • Remove soft objects like stuffed toys from the bedroom
  • Keep humidity levels low, ideally at 30 to 50 percent with a dehumidifier
  • Have other people dust and vacuum your home
  • Wear a face mask while cleaning your home


Mold makes spores that get into the air and trigger allergic reactions. It is usually found in moist places, such as basements and bathrooms. About half of homes have enough mold to trigger allergy and asthma symptoms.3

Ways to reduce exposure to mold in your home include:4

  • Dry wet items quickly
  • Fix water leaks
  • Replace absorbent materials if mold is present
  • Use a dehumidifier to lower humidity in rooms
  • Run the exhaust fan in the bathroom during and after showers and baths


Pollen is a powdery substance that comes from plants. Most plants produce pollen, but people tend to react to the pollen that is light enough to float through the air. Pollen on plants like flowers is heavier and is generally spread by bees and other insects, not the wind.1,2

Grass, tree, and weed pollen are the most common types that trigger allergies and asthma. Some pollen allergies are seasonal. This means they flare up at a certain time of year. There are regional differences, but generally trees release the most pollen in the spring, grasses in the summer, and ragweed in the fall.1,2

Ways to reduce exposure to pollen include:6

  • Check the forecast and stay indoors on days when the pollen count is high
  • Stay indoors between 5 and 10 am, when pollen counts are usually highest
  • Keep windows closed at home and in your car
  • Wear a mask when gardening or mowing the lawn, or avoid mowing or being around freshly cut grass
  • Avoid raking leaves or working with hay or mulch
  • After being outdoors, take a shower and wash your hair to remove pollen that may have landed on you


Cockroaches are pests found in homes and other buildings. The saliva, feces, and other body parts of cockroaches can trigger allergies and asthma. Cockroaches are very common in urban homes and buildings. Between 60 and 80 percent of children with allergies are sensitive to cockroach allergens.3-7

Tips to reduce exposure to cockroaches focus on taking away their sources of water and food and include:4-7

  • Clean dishes, crumbs, and spills immediately
  • Keep food out of the bedroom
  • Store food in airtight containers
  • Keep trash in a closed container
  • Keep counters, tables, and floors free of clutter
  • Seal cracks or openings in cabinets and walls
  • Use traps in areas away from children and pets
  • Avoid using insect sprays, which may also cause asthma attacks