Indoor Allergens

  • Medical Author: Rick Kulkarni, MD
  • Coauthor: Kathryn L Hale, MS, PA-C
  • Medical Editor: Richard F Lockey, MD
  • Medical Editor: Mary L Windle, PharmD
  • Medical Editor: Timothy D Rice, MD
Reviewed on 1/6/2022

What Facts Should I Know About Indoor Allergens?

Indoor allergy
The usual symptoms and signs of indoor allergic reactions are those of many other allergic reactions.

Most people with asthma or hay fever or other outdoor allergies think of their home as a haven where they can escape their allergies. Unfortunately, houses and apartment buildings harbor their own allergens (agents that cause allergy symptoms). The inside of your home actually traps allergens, making them impossible to avoid.

What are the most common indoor allergens?

Although many allergens in your environment can trigger allergic symptoms, house dust is the main culprit in indoor allergies. What is house dust?

  • It varies depending on the type and age of your home, the temperature and humidity in the home, what you keep in the home (everything from food to clothes to furniture), and who lives in the home (human, pet animal, and plant).
  • Some dust is present in every home, regardless of how often or how thoroughly the house is cleaned.
  • House dust is an airborne mixture that might contain fine particles of soil and plant material from indoors or outdoors, particles of human and animal skin (dander) and hair, fabric fibers, mold spores, dust mites, fragments of insects that have died and their waste, food particles, and other debris.
  • Although many substances in dust can trigger allergic symptoms, the most important indoor allergens are dust mites, pet dander, cockroaches, and molds.
  • Unlike seasonal allergies such as hay fever, indoor allergies may last all year long. Indoor allergens may provoke or worsen asthma symptoms, depending on a person's unique sensitivities.
    • Indoor allergies tend to be at their worst in the late summer when dust mites are at their peaks.
    • Allergy symptoms can actually be worse in the winter when the windows are closed and people are shut in with the allergens.
    • Keeping your windows open at night during seasons of high outdoor pollen and mold count may worsen your allergy symptoms or asthma because these high-concentration outdoor allergens are allowed into your house to settle.
    • If you are sensitive to indoor allergens, you will continue to have symptoms as long as you are exposed to your allergens.

Who is at risk for indoor allergens?

  • Sensitivity to indoor allergens is very common and occurs at every age. It is less common in children younger than 5 years. People most likely to experience allergic rhinitis are those in early school and early adult years.

What Causes Indoor Allergies?

An allergic sensitivity is a reaction of the immune system to a foreign "invader," a substance that is not native to your body. Exposure to this invader, an allergen, triggers the reaction.

When the allergen particles come to rest in the linings of the eyes, nose, or airway of a susceptible person, an allergic reaction can occur.

  • When the immune system has been previously "sensitized" to a specific invader, it overreacts to the invader; this overreaction to a harmless substance is known as a hypersensitivity or allergic reaction.
  • This reaction sets in motion a series of responses that culminates in release of chemicals called "mediators." Histamine is an example of a mediator.
  • It is the effects of the mediators on cells and tissues that cause allergic symptoms.

Dust mites

  • Dust mites are common indoor allergens. They can be found in most homes, usually in beds and bedding, upholstered furniture, or any cloth material.
  • Often, when people believe they are sensitive to dust, they are actually sensitive to the dust mites and their waste particles and fragments of dust mites that have died that can be found in household dust.

Pet dander

  • For some people, pets trigger allergic reactions. They simply cannot be around animals such as dogs, cats, gerbils, hamsters, and other fur-bearing animals without developing uncomfortable symptoms such as sneezing, stuffy nose, itchy eyes, and asthma.
  • Contrary to what many people believe, an allergic reaction to an animal is not caused by the animal's hair.
    • An allergic reaction is actually caused by substances in the animal's saliva, urine, and especially dander.
    • Dander is dead skin flakes (like dandruff) that become loosened from the animal's skin.
    • The allergens become crusted on the animal's hair or skin from urination or the animal licking or scratching itself; once dry, the allergens are released into the air, where they join the other components of house dust.
  • Many different small animals that are popular as house pets trigger allergic reactions.
    • Animals such as cats and dogs are most likely to cause allergic reactions.
    • Birds may also cause reactions, although less often than other animals.
    • Animals such as fish, reptiles, and amphibians rarely cause allergic reactions.
  • An allergic reaction may be triggered by any of the following:
    • Directly touching the animal
    • Being in an indoor area with the animal
    • Being in an indoor area with furniture, carpets, bedding, drapes, clothing, animal beds or cages, even countertops and walls on which animal allergen has landed
    • Being in an indoor area with another person whose clothes carry the allergen
    • Cleaning animal beds, cages, or litter boxes
    • Touching toys, bedding, towels, or other items that the animal has touched


  • Molds are a type of fungus that has no stems, leaves, or roots.
    • Molds generally live outdoors but can normally be found in almost any indoor environment. They can trigger hay fever and asthma symptoms and reproduce by releasing spores into the air, which float around until they find a hospitable environment.
    • They easily pass through open doors and windows and settle indoors, especially where there is excess heat and humidity. They grow and produce mildew. Many of us have seen mildew growing in a shower.
    • Mold is not always visible, however; it can grow in unseen areas of the house, such as under flooring materials and behind walls.
  • To grow, mold requires water; this can be either liquid water, as from a leaky pipe or roof or a puddle, or condensation on windows.
    • It also requires something to grow on, and mold is not picky, although it is most likely to grow on wood, sheet rock, or fabric.
    • As it grows, mold releases more spores, many of which become part of house dust.
  • While molds can trigger allergic symptoms, like any other allergen, they rarely cause serious health problems, except in people who are seriously immunocompromised or on chemotherapy.


  • Most of us don't want to think about insects in our home, especially cockroaches, but they are a fact of life. If you live in a crowded urban area, an older multifamily dwelling, or a warm climate such as the southern part of the United States, you almost surely have cockroaches living in your home, even if you don't see them.
  • Cockroaches like moist places where food is available.
    • Although the kitchen is their favorite room, they can be found just about anywhere in the house.
    • When they die, usually not in plain sight, their bodies become dried and break apart. These body pieces, as well as their dried waste, become part of house dust.

What Are Indoor Allergy Symptoms and Signs?

The usual symptoms of indoor allergic reactions are those of many other allergic reactions:

  • Itchy, stuffy nose
  • Clear nasal discharge
  • Itchy, watery, swollen, bloodshot eyes
  • Sneezing
  • Scratchy, swollen throat
  • Cough
  • Wheezing
  • Tightness in the chest
  • Reactions to animal allergens may be very mild or quite severe. Symptoms may occur immediately after exposure to the allergen, or they may build gradually for 8-12 hours after exposure or become persistent.

When to Seek Medical Care for Indoor Allergies

If the symptoms of the allergic reaction worsen or do not improve with removal of the allergen, call a physician. If you are having persistent nasal, eye, or chest symptoms, see your doctor. If your respiratory problems are severe (e.g., shortness of breath, difficulty breathing), go to the emergency department or seek care from your physician as soon as possible.

What Exams and Tests Diagnose Indoor Allergens?

Generally, your physician will be able to identify the problem by examining you and asking questions. Treatment can begin without further evaluation or testing.

Tests and X-ray films are not required except under unusual circumstances.

If you don't respond well to treatment or if there is any doubt about what is causing the reaction, an allergy specialist (allergist) can use skin tests that may identify the allergen. Many people find this worthwhile before going through elaborate procedures to remove allergens from their home or making the painful decision to get rid of a pet.

What Are Indoor Allergy Treatments?

The single best thing you can do is remove the allergen from your environment (see Prevention). A variety of medications can be used to treat hay fever, eye symptoms, and asthma.

Are There Home Remedies for Indoor Allergies?

Nonprescription antihistamine medication such as diphenhydramine (Benadryl) by mouth reduces the itch and watery eyes. Caution...These medications may make you too drowsy to drive or operate machinery safely. They can interfere with concentration or with children's learning at school. They are to be used for a few days only.

What Is the Medical Treatment for Indoor Allergies?

If symptoms do not improve, your physician may prescribe one or more medications. The medications do not cure the allergy, but relieve symptoms.

What Medications Treat Indoor Allergies?

  • Antihistamines include older antihistamines, also called first-generation antihistamines, and newer second-generation antihistamines.
    • First-generation antihistamines: Most of these antihistamines are available without a prescription, such as diphenhydramine (Benadryl), clemastine (Tavist), and chlorpheniramine (Chlor-Trimeton Allergy). These older antihistamines are more likely to cause drowsiness. Depending on the product, the duration of action is often shorter than newer antihistamines and may necessitate taking the drug 3-4 times each day. These older antihistamines are more likely to cause dry mouth, urinary retention, constipation, and blurred vision.
    • Second-generation antihistamines: These antihistamines are also referred to as nonsedating antihistamines. Most are available over the counter, such as cetirizine (Zyrtec), desloratadine (Clarinex), and fexofenadine (Allergra). They can be taken over the long term with minimal side effects and are unlikely to cause sleepiness. The nonsedating antihistamines are convenient to take since they are taken once or twice daily. They may allow you to carry on with your normal activities more easily than older first-generation antihistamines.
  • Decongestants are also available to decongest the nose when it is stuffy. Do not use decongestant nose sprays (such as Afrin) for more than 3 days, otherwise nasal congestion will reoccur.
  • Anti-allergy eyedrops: These may relieve severe itching, tearing, redness, or swelling of the eyes.
  • Corticosteroid nasal spray usually works better than do antihistamines. Corticosteroid nasal sprays relieve the congestion and swelling of the lining of the nose. These sprays take a few days to work and are best used every day to be most effective. They are safe to use because so little medicine is necessary for relief.
  • Corticosteroids (such as prednisone, methylprednisolone) are prescription medications taken by injection or by mouth that reduce inflammation and symptoms such as swelling.
  • Mast cell inhibitors, such as cromolyn sodium nose spray and eyedrops, may also be used to prevent histamine release and provide treatment locally for runny nose or watery eyes.
  • Leukotriene inhibitors, such as montelukast (Singulair) are starting to be used to prevent allergic symptoms. These are particularly useful for individuals whose asthma is easily triggered by allergies.

See Understanding Allergy and Hay Fever Medications for more information.

Other Therapy for Indoor Allergies

Allergy shots: These are given to some people who have persistent and disruptive allergy symptoms.

  • The shots do not treat symptoms, but by altering the immune response, they prevent future allergic reactions. (This is referred to as allergen immunotherapy.)
  • Treatment involves a series of shots, each containing a slightly greater amount of the allergen(s) that cause the reaction.
  • Ideally, the person will become "desensitized" to the antigen(s) over time.

Indoor Allergen Follow-up

If your symptoms are severe enough or last long enough to require treatment by a medical professional, follow his or her treatment recommendations. Take all prescribed medications as directed.

Is It Possible to Prevent Indoor Allergies?

The single best thing you can do to stop the reaction is to reduce your exposure to the allergens.

If it is animal dander causing your allergic reaction, you do have options.

  • Keeping the animal outdoors all the time is a partial solution, but your home will still have greater amounts of dander than if the animal is removed altogether.
  • You may want to see an allergist to confirm that your pet is the cause of the symptoms before making the painful decision to get rid of a pet.
  • If you decide to remove the animal, it may take as long as 6 months or longer for the allergy symptoms to go away completely.

If you decide to keep the pet and live with your allergy, have as little direct contact with the pet as possible.

  • Another family member should have responsibility for grooming, feeding, exercising, and cleaning up after the pet.
  • Keeping the pet well groomed may help reduce the amount of dander in the household. Beware, though, of bathing the pet too often, which can damage the skin and worsen the dander problem. Consult with the pet's veterinarian for tips on keeping the animal as dander-free as possible.
  • Keep the pet out of the rooms where you spend most of your time, especially your bedroom.
  • Minimize the impact of dander by living with as little carpet, upholstered furniture, and drapes as you can manage.
  • Cover your mattresses, box springs, and pillows with covers that prevent release of allergens.

Before getting a pet, spend indoor and outdoor time with other animals of the same species to make sure all family members can tolerate the dander. Remember that allergies tend to run in families. If you are allergic to animal dander, your children may be too. Also, even people who do not have problems initially may develop them later.

It is practically impossible to remove all house dust with all its allergens from your home.

  • Shampoo or replace carpets. Better yet, remove the carpet. Smooth floors collect fewer allergenic particles.
  • Clean or replace bedding.
  • Clean or remove upholstered furniture
  • Clean floors, walls, and surfaces such as windowsills, window shades, countertops, cabinets, and other doors
  • Launder or dry clean drapes, including those in storage
  • Launder all clothes, towels, and other household items, including those in storage

Consider seeing an allergist for allergy shots. Allergy shots can reduce your sensitivity to indoor allergens.

What Is the Prognosis for Indoor Allergies?

In almost everyone who has an allergic reaction to house dust, symptoms will improve with treatment.

If the allergy is to animal dander, removal of the animal will result in gradual disappearance of symptoms.

  • You may notice significant improvement in 2-3 weeks, but it may take 6 months or longer for your symptoms to resolve.
  • The vast majority of people with animal dander allergy are able to avoid uncomfortable allergic symptoms simply by avoiding the animal sources of their allergens.
  • Unfortunately, this sometimes means avoiding the homes of friends with pets and public places where animals go.
  • With so many dogs, cats, and other pets in our world, you are bound to be exposed to dander occasionally.

For More Information on Indoor Allergies

American Academy of Allergy, Asthma & Immunology

National Institute of Allergy and Infectious Diseases (NAIAD), Allergies

Reviewed on 1/6/2022
Medically reviewed by Michael Manning, MD; American Board of Allergy & Immunology


"Allergen avoidance in the treatment of asthma and allergic rhinitis."