Airborne allergens can affect you whether you are indoors or outside

Indoor and outdoor airborne allergens: what are they and how to prevent them

Medically reviewed by Rosanna Sutherby, PharmD on March 24, 2020. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Table of contents

Each year, over 50 million people around America suffer from allergies—making allergies the 6th leading cause of chronic illness in the United States.

From itchy eyes and a runny nose, to the more severe reactions like chest pains, airborne allergies cause unpleasant symptoms for many of us. If your allergies are acting up, it might be time to take a closer look at what allergens are in the air today. From outdoor allergens like pollen to common indoor allergens like dust mites, allergens in the air can have different effects on those who come into contact with them.

Thankfully, once you identify what’s triggering your allergy symptoms—our at-home allergy test can help with that—you can take steps to reduce your exposure to triggering allergens and ease your symptoms.


Common indoor airborne allergens

Dust mites

House dust is a mixture of cotton, lint, feathers, dander, food, and more—and one common cause of airborne allergies from house dust is dust mites. Dust mites thrive in warm and humid environments and can be found in bedding, upholstered furniture, drapes, and carpet. They’re microscopic organisms, so you can’t see them with the naked eye (though if you’re allergic, you can certainly feel their effects on your sinuses).

Indoor mold

Indoor molds produce allergens in the air that can lead to reactions in some people. Indoor mold and mildew are often found in bathrooms, basements, or places with leaks. It can also come from indoor plants, particularly those that are kept in damp wicker baskets. Mattresses, old foam rubber pillows, closets, and furniture can also offer a home for indoor mold growth.

Pet allergens

Household pets are another familiar cause of airborne allergies, but why do pet allergies occur? When an animal sheds its skin, dander is produced, which can be a cause of allergic reactions. Pet saliva and urine also are sources of allergy-causing proteins, which means when a cat licks itself then gets close to someone, it can be a cause of an allergic reaction. Like dogs and cats, other animals like guinea pigs and gerbils can produce indoor allergens in the air—as can mice and rats.

Time of year for indoor allergens

Although indoor allergens can affect you any time of year, your symptoms are likely to act up in the winter when you’re spending more time indoors. As people turn their heaters up, particles from pet dander and dust are blown around, which irritates the sinuses. The indoor air is dry because of the heater, which can cause the nasal passages to inflame and be more prone to allergy irritation.

Keep in mind that winter is also a time for colds, which can closely resemble allergy symptoms. Aches and fever generally are not a symptom of allergies—and itchy, watery eyes are not a symptom of a cold. Indoor allergens can also exist in the air during the spring and summer months when the windows are open and a breeze causes pollen to get inside and land on furnishing and carpet.

Common outdoor airborne allergens


If you asked what allergens are in the air today, many people would respond, "Pollen!" During the spring, summer, and fall, plants like trees, weeds, and grasses release pollen grains. These tiny grains move through the air in an effort to fertilize plants, though many of them land in our noses and throats, which can cause a sore throat and runny nose.

Pollen is one of the most common outdoor airborne allergens, and when the pollen count in the air is high, it’s a hard one to avoid. Pollen can be produced by grasses, like Timothy grass Kentucky bluegrass, and orchard grass (to name a few). It can also come from trees like oak trees, elm trees, and pecan trees. Pollen is often one of the main causes of spring allergies and can lead to many uncomfortable symptoms.

Outdoor mold

Outdoor mold, like its indoor counterpart, also produces allergens in the air. Similar to how trees release pollen, mold releases spores. When a breeze comes along, spores are spread and cause allergy symptoms. Outdoor molds include molds like Alternaria, Cladosporium, and Hormodendrum.

Time of year for outdoor allergens

Outdoor allergens tend to coincide with tree and grass pollination, as this is the time when pollen is dispersed. In many parts of the United States, allergy season can begin in the early spring and last through the fall. This can fluctuate depending on temperatures and rainfall. A mild winter might cause plants to pollinate early, and a rainy spring can lead to quick plant growth (and an increase in outdoor mold as well).

Symptoms of airborne allergies

The symptoms of airborne allergies are often uncomfortable, frustrating, and—unfortunately—familiar to many people. When an airborne allergen lands on the lining of the inside of the nose, a reaction occurs that leads the tissues' cells to release histamine and other biochemicals. The biochemicals contract cells that line the blood vessels in the nose, which causes fluid to escape. When the fluid escapes, the nasal passages swell which results in congestion.

The release of histamine can also cause symptoms like itching, irritation, and more. Here are some of the common symptoms brought on by allergens in the air.


Sneezing is common to those of us who suffer from airborne allergies. Often, the sneezing is accompanied by a runny or clogged nose.


Coughing, although sometimes a sign of a cold, can also be an allergic response to airborne allergens if they cause postnasal drip. Postnasal drip happens when your body produces too much mucus and can feel like a tickle in the back of the throat (caused by the mucus moving down the nose and throat).

Itchy eyes, nose, and throat

Itchy eyes, nose, and throat are another common symptom brought on by airborne allergies.

Watering eyes and conjunctivitis

Watering eyes and conjunctivitis—or pink eye—are also forms of irritation caused by allergies.

Dark circles under the eyes

Also called “allergic shiners,” dark circles under the eyes are caused by an increased blood flow near the sinuses.

How to prevent the effects of airborne allergies

Indoor allergies

Keep things clean

One important step for reducing airborne allergies is making sure you keep your home clean. Although a dust mite allergy can occur even when homes are clean, it’s a good rule of thumb to do a deep cleaning to help eliminate dust as well as pollen and pet dander.

Use a humidifier

Because dry air can take away the protective layer of mucus in your sinuses, it can amplify irritation due to allergies. Use a humidifier to keep the humidity level in your home at about 40% or so.

Try an air filter

Air filters help capture allergens in the air like dust, pollen, and pet dander.

HEPA Vacuum Cleaners

HEPA filter vacuums are effective cleaning systems and can help reduce your allergy symptoms. Remember to clean furniture, curtains, and drapes in addition to floors and walls.


If possible, get rid of wall-to-wall carpet and invest in hardwood or tile floors instead, as this will help decrease the collection of dust, dander, pollen, and mold.

Heating and air conditioning

Heating and air conditioning vents can suck up indoor pollutants and redistribute them. Cover the vents with a filtering material and change the system filters frequently.

Wash your hands

Whether you’re inside or outside, washing your hands is crucial because it helps eliminate the spread of airborne allergens from your fingertips to your eyes.

Outdoor Allergies

When it comes to outdoor allergies, there are several things you can do to prevent the effects of allergens in the air.

Stay inside

Allergen counts are typically lower later in the day. If possible, stay inside in the morning when the allergen counts are high.

Wash your clothing

Washing your clothes can help get rid of pollen that’s stuck to the fibers. If pollen causes symptoms for you, it’s also a good idea to avoid hanging clothes on the outdoor clothesline during months when pollen can gather on them.

Close your windows

Whether you’re driving in the car or sitting in a sunny spot on the couch, it’s a good idea to keep windows closed so that allergens in the air can’t get in and irritate you.


Every year, allergens in the air cause discomfort for millions of people nationwide. By recognizing the common indoor and outdoor allergens, you can take steps to proactively reduce your exposure. Cleaning, washing your clothing, and making sure to eliminate dust and mold from places like carpet and walls can be a good step toward becoming allergy-free.

Allergies can come sneaking up any time of year—and the symptoms can vary greatly depending on who they’re affecting. If you’re experiencing some of the symptoms listed above, but aren't sure what allergen(s) is the cause, consider taking our at-home allergy test to help you find out which airborne allergies may be affecting you.

We’re exposing indoor and outdoor allergies

How to welcome the spring season without the allergy attacks

5 ways to prevent dust mite allergies

Pet allergies: causes, symptoms, and remedies

Indoor vs. outdoor allergies: top tips for managing symptoms

Is it a cold or allergies?

Fact or fiction? Top 5 truths about allergies you need to know


1. Allergy Facts. American College of Allergy, Asthma & Immunology. URL. Accessed March 13, 2020.

2. Indoor Allergens. American Academy of Allergy, Asthma & Immunology. URL. Accessed March 13, 2020.

3. Cold, Flu, or Allergy? NIH News in Health. URL. Published 2014. Accessed March 31, 2020.

4. Seasonal Allergies. American College of Allergy, Asthma & Immunology. URL. Accessed March 13, 2020.

5. Control Indoor Allergens to Improve Indoor Air Quality. Asthma and Allergy Foundation of America. URL. Accessed March 31, 2020.

6. Allergy-proof your home. Mayo Clinic. URL. Accessed March 31, 2020.

7. Pet Allergy: Are You Allergic to Dogs or Cats? Asthma and Allergy Foundation of America. URL. Accessed March 31, 2020.

8. Seasonal allergies: Nip them in the bud. Mayo Clinic. URL. Accessed March 31, 2020.

Everlywell makes lab testing easy and convenient with at-home collection and digital results in days. Learn More