Indoor allergy (perennial allergic rhinitis)

18 min read

What is an indoor allergy?

An indoor allergy is when something in your home or work environment triggers an allergic reaction that causes the lining of your nose to become inflamed.

This can cause cold-like symptoms such as:

  • sneezing
  • a runny nose
  • nasal congestion


symptoms of an indoor allergy
can range from mild to severe. While an indoor allergy doesn't pose a serious threat to your health, it can have a considerable impact on your quality of life. It can affect sleep, daily activities and performance at work or school.

An indoor allergy is also known as perennial allergic rhinitis. The symptoms can occur all year round, unlike the seasonal types of

allergic rhinitis
, such as
hay fever
, which is caused by an allergic reaction to certain types of pollen.

However, some allergens inside the home can trigger the symptoms of hay fever as well as other conditions such as


In some cases an indoor allergy can contribute to

, a condition where the sinuses become inflamed or infected. Read about the
complications of an indoor allergy

What causes an indoor allergy?

Anything that causes an allergic reaction is known as an allergen. The most common triggers of indoor allergies are:

  • dust mites
  • fungus spores
  • pets, in particular the dead skin that is shed by pets (known as animal dander)
  • substances related to particular occupations or workplaces, such as wood dust and chemicals

Read more about the

causes of an indoor allergy

Treating indoor allergies

Medication to help manage the symptoms of an indoor allergy is available over the counter at pharmacies or on prescription. This includes:

In some cases, the symptoms of an indoor allergy can be reduced by using a treatment called immunotherapy. This involves exposing the affected person to small amounts of whatever they are allergic to over time so that their body builds up a tolerance to the allergen.

However, immunotherapy is time-consuming, taking three to five years to complete. It's also not suitable for everyone.

Read more about

treating indoor allergies

Preventing indoor allergies

The best way to

prevent indoor allergies
is to avoid whatever is causing the allergic reaction. However, this is not always possible and extra steps might be needed, such as:

  • replacing carpets with hard wood flooring
  • minimising contact with pets
  • regularly checking for signs of fungal mould

Who is affected by indoor allergies?

Indoor allergies are very common. It is estimated that 10%-20% of the population has an indoor allergy.

Most indoor allergies first develop during childhood or early adulthood, with 80% of cases developing before a person reaches the age of 20.

Men and women are equally affected by indoor allergies.

Indoor allergy symptoms

The symptoms of an indoor allergy are like having a cold. They happen at any age and any time of year, unlike seasonal allergies such as hay fever.

However, some allergens inside the home can trigger the symptoms of

hay fever
as well as other conditions such as eczema.

The symptoms of an indoor allergy usually have two phases:

  • the early phase, which happens within minutes of being exposed to the allergen
  • the late phase, which happens four to eight hours after exposure

The early phase

The early-phase symptoms of indoor allergy include:

  • sneezing
  • runny nose
  • blocked nose (nasal congestion)
  • itchiness and irritation of your eyes, nose and throat
  • itchy skin or rashes
  • facial pain
  • tightness in the chest
  • headache

The late phase

The late-phase symptoms of indoor allergy are similar to those of the early stage, but with less sneezing and itching. The symptoms of nasal congestion also get worse and you may find yourself producing a lot of mucus.

In a small number of people, the nasal congestion is so severe that they lose some of their sense of taste and smell. The late phase can continue for hours or days.

Over time, repeated allergic reactions can lead to more generalised symptoms, such as:

  • fatigue
  • feeling very sleepy
  • a general sense of feeling unwell

Causes of indoor allergies

Indoor allergies are caused when the immune system, the body's natural defence system against infection, reacts to certain substances as if they were harmful.

The immune system produces antibodies to fight off the allergen. Antibodies are special proteins in the blood that are created by the immune system to fight off harmful viruses and infections.

When small particles of an allergen come into contact with the inside of your nose and throat, an antibody called Immunoglobulin E (IgE) is released. IgE causes other blood cells to release more chemicals (including histamine) which, together, cause the

symptoms of an allergic reaction

Histamine causes most of the symptoms of an allergic reaction, such as:

  • swelling of the inside layer of your nose (the mucus membrane), which blocks the airway and causes congestion
  • the production of excess mucus, which occurs as a result of the swelling and causes a runny nose and sneezing

It is still unclear why people develop over-sensitivity to allergens. However, there seems to be a genetic link (it may run in families). Exposure to cigarette smoke during childhood also seems to increase the risk.

Indoor allergens

An indoor allergy is triggered when you breathe in small particles of an allergen. Some common causes of indoor allergies are described below.

House dust mites

House dust mites are tiny insects that feed on the dead flakes of human skin. They can be found in:

  • mattresses
  • carpets
  • soft furniture
  • pillows
  • beds

Indoor allergies aren't caused by the dust mites themselves, but by a chemical found in their faeces (stools). Dust mites are present all year round. It's estimated that one square metre of carpet could contain around 100,000 mites. Their numbers usually peak during spring and autumn, so your symptoms may be more troublesome during these times.


Household pets can often trigger an indoor allergy. Dogs and cats are the most common cause, although some people are affected by rabbits, guinea pigs, hamsters and birds.

It’s usually the flakes of dead animal skin or the animals’ urine and saliva that are responsible for an allergic reaction, and not the fur or feathers.

Some indoor allergies can be triggered by an infestation of pests, such as mice or cockroaches.

Fungal moulds and spores

Fungi are plant-like organisms. Unlike plants, they can't produce food using sunlight (photosynthesis). To feed, fungi break down natural materials, such as wood, by growing into the material. These growths are known fungal moulds.

Fungal moulds can grow anywhere inside your house where there is natural material, such as wood, paper, food, plants and some types of insulation.

Fungi particularly thrive in warm, damp areas, such as:

  • the bathroom
  • the kitchen
  • around pipes and boilers
  • basements

The moulds themselves do not cause the allergic reaction, but they can release tiny spores into the air which can be swallowed, triggering an allergic reaction.

Occupational allergies

Several allergens found in certain workplaces can trigger an indoor allergy. These include:

  • chemicals, which can affect people who work in manufacturing plants and factories, or other areas such as hairdressing
  • wood dust, which can affect carpenters or joiners
  • latex, which can affect healthcare workers
  • animals, which can affect veterinarian and agricultural workers, as well as people who work in laboratories
  • flour dust, which can affect bakers and people who work in catering

Diagnosing indoor allergies

Your doctor should be able to diagnose an indoor allergy by asking you about your symptoms and your personal and family medical history.

They will also ask you about any allergens that seem to cause a reaction, and whether the reaction occurs at a particular place or time. If your symptoms only develop when you're at home or at work, it's very likely that they are the result of an indoor allergy.

Physical examination

Your doctor may examine the inside of your nose to check for the presence of

nasal polyps
. Nasal polyps are fleshy swellings that grow on the lining of the nose or sinuses (small air-filled cavities inside your cheekbones and forehead). Polyps are caused by the inflammation associated with an indoor allergy.

Your doctor may also recommend that you take

(a widely used anti-allergy medication) to see whether your symptoms improve. If your symptoms do improve, it's very likely that they were caused by an allergic reaction.

After asking about your allergy history, your doctor may carry out tests to identify the allergen that is causing your symptoms, or refer you to a specialist at an allergy clinic.

Allergy testing.

Even if you think you know what is causing the allergic reaction, you may need to be tested to determine the exact allergen and get a definite diagnosis.

The type of test you are offered will depend on your symptoms, the condition of your skin and any medication you are taking. Possible tests include:

  • Skin prick test. This is usually the first test to be done when looking for an allergen. The skin is pricked with a tiny amount of the suspected allergen to see if there is a reaction. If there is, the skin around the prick will very quickly become itchy, red and swollen. Because the skin prick test introduces such a tiny amount of allergen into the skin, it’s considered very safe and can be used on almost any age group, including babies. However, it may not be suitable if you have a history of severe reaction to an allergen.
  • Blood test. This is used to measure the amount of IgE antibodies in your blood that have been produced by your immune system in response to a suspected allergen. The results are given on a scale from zero to six: zero indicates a negative result and six indicates an extremely high sensitivity.
    Blood tests
    are particularly useful when you are at risk of an extreme reaction or when a rare allergen is suspected.
  • Patch test. This test is used to find an allergen causing eczema (contact dermatitis). A small amount of the suspected allergen is added to special metal discs, which are then taped to your skin for 48 hours and monitored for a reaction. This test is usually carried out at a dermatology (skin) department in a hospital.

The use of commercial allergy testing kits is not recommended. These tests are often of a lower standard than accredited clinics. Also, allergy tests should be interpreted by a qualified professional who has detailed knowledge of your symptoms and medical history.

Treatment for an indoor allergy

There are several types of medication available to manage the symptoms of an indoor allergy.


The three medications most widely used to treat an indoor allergy are:

Nasal decongestants

Nasal decongestants are usually available over-the-counter (OTC) in the form of a nasal spray. Only use a decongestant spray for short-term relief of your symptoms. Using the spray for longer than five to seven days may make your symptoms worse.

If you're taking a type of antidepressant known as a monoamine oxidase inhibitor (MAOI), do not use nasal decongestants. The combination of the two types of medication can cause serious side effects.


Antihistamines are usually recommended as the initial treatment for a mild to moderate indoor allergy.

Antihistamines block the action of the chemical histamine, which the body releases when it thinks it is under attack from an allergen. Antihistamines can be taken as a tablet (oral), as nasal sprays or drops (topical intranasal).

Oral antihistamines are available over-the-counter (OTC) without prescription from your pharmacist. Antihistamine nasal sprays are only available with a prescription. Oral antihistamines are not suitable for children under two years of age and antihistamine nasal sprays are not suitable for children under five years of age.

In the past, antihistamines caused drowsiness, but new types were developed to avoid this side effect. However, around 10% of people are still affected by drowsiness.

If during the night your symptoms are particularly troublesome, you may prefer to take an older type of antihistamine because the side effect of drowsiness may help you to sleep better.

If you're taking antihistamines, see how you react to the medication before driving or operating heavy machinery. Antihistamines can cause drowsiness if you take them, especially if you drink alcohol.

You can take antihistamines if you are pregnant. However, to minimise any risk to your unborn child, it's recommended that you use a nasal spray rather than tablets. Older antihistamines, such as

and cetirizine, are preferred to newer medicines because there is more information available about their safety.


If your symptoms are frequent or persistent and you have a nasal blockage or

nasal polyps
, your doctor may recommend that you use a nasal spray which contains corticosteroids (topical intranasal corticosteroids), either as a single treatment or in combination with antihistamines.

Corticosteroids block many of the functions of the immune system and also help to reduce inflammation. They take longer to work than antihistamines, but their effects last longer.

Side effects from inhaled corticosteroids are rare, but can include dryness and irritation of the nose, and nose bleeds.

If you need fast relief from your symptoms, you may be given a short-term course of oral antihistamines to take in combination with your corticosteroid nasal spray.

If your symptoms are severe and you're worried that they will have an impact on an important event, such as a driving test or exam, let your doctor know. They may recommend taking a seven-day course of oral corticosteroids to control your symptoms.

The use of oral corticosteroids on a long-term basis isn't usually recommended. Long-term use can cause a range of side effects, such as weight gain and thinning of the skin.


Immunotherapy, sometimes known as hyposensitisation, involves gradually increasing your exposure to an allergen to make you less sensitive to it. It makes you less likely to react adversely to the allergen when you are exposed to it in the future.

Immunotherapy has proved particularly effective in treating people with an allergy to:

  • cats
  • dust mites
  • fungal spores
  • cockroaches

As immunotherapy involves a three- to five-year course of treatment, it is usually only recommended if your symptoms cannot be controlled with medication.

Immunotherapy may not be suitable for you if you have:

  • severe
  • a weakened immune system, either as a result of a condition, such as
    , or due to a side effect of a medical treatment, such as
  • a serious health condition, such as
    heart disease

There are two main ways that immunotherapy is used:

  • subcutaneous immunotherapy, where you are given regular injections of the allergen into your skin
  • sublingual immunotherapy, where you are given a small capsule containing a sample of the allergen, which you dissolve under your tongue

Evidence suggests that subcutaneous immunotherapy may be more effective at relieving the symptoms of an allergy, although sublingual immunotherapy may be your preferred option if you don't like having regular injections.

It will usually take between six and twelve months before you notice an improvement in your symptoms.

There is a small risk of immunotherapy treatment triggering a serious allergic reaction known as anaphylaxis. Read more about the

complications of indoor allergies

Preventing indoor allergies

The best way to prevent an allergic reaction is to avoid the offending allergen. However, this may not always be possible every day.

The following advice may help you limit your exposure to the offending allergen as much as possible.

Dust mites

Dust mites are probably the hardest indoor allergen to avoid. Keeping your house free from them is difficult, requires long-term commitment and can be very expensive.

There is also limited evidence to suggest that eradicating dust mites from your home is an effective way of reducing or preventing symptoms of an indoor allergy.

If you want to reduce the number of dust mites in your home, you may find some of the following techniques useful.

  • Put down wood or hard vinyl floor coverings instead of carpet.
  • Instead of curtains, fit roller blinds which can be easily wiped clean.
  • Remove cushions, soft toys and other upholstered furniture.
  • Use synthetic pillows and acrylic duvets instead of woollen blankets or feather bedding.
  • Wash bedding weekly using a hot wash of 55C-60C (131F-140F).
  • Use a vacuum cleaner that is fitted with a high-efficiency particulate air (HEPA) filter, which can remove more dust than an ordinary vacuum cleaner.
  • Wipe surfaces using a damp, clean cloth, as dry dusting can spread the allergens further.
  • Dust inside cupboards as dust can settle on the objects inside.


Giving up your pet is the most effective way to prevent exposure to this type of allergen. This can obviously be a difficult decision for many people to make.

If your personal circumstances prevent you from permanently removing your pet from the house, you may find the following advice useful.

  • Keep pets outside as much as possible, or limit them to one room, preferably one without carpet.
  • Don't allow pets in bedrooms, because their skin flakes can remain in the air for a long time.
  • Wash pets at least once a fortnight (ideally, twice a week).
  • Install a HEPA air filter.
  • If possible, remove carpets and replace them with wooden or hard vinyl floor coverings.
  • Castration (removal of some or all of the male reproductive organs so that the animal is unable to breed) will reduce the production of allergens by male cats and dogs.

Fungal moulds and spores

The following advice may help you limit your exposure to fungal moulds and spores.

  • Keep your windows closed to prevent spores from coming in from the outside.
  • Use a dehumidifier to reduce the moisture in your house.
  • Install a HEPA air filter.
  • Replacing carpets with wood or hard vinyl floor coverings should help reduce the amount and spread of spores.
  • Strip wallpaper from damp walls.
  • Get rid of old foam pillows and mattresses.
  • Do not leave food out to decay.
  • Regularly inspect high-risk areas for fungal contamination, such as your basement and around pipes, radiators, boilers and air conditioning units.
  • Use a fungicide spray or cream to remove any contamination.

Complications of an indoor allergy

If someone with an indoor allergy is regularly exposed to allergens, this can affect the sinuses.


, a common complication of an indoor allergy, is inflammation or infection of the sinuses (small air-filled cavities that are located inside the cheekbones and forehead).

This can happen if your sinuses become filled with mucus (fluid) which is unable to drain away, for example due to a blockage, and becomes infected with bacteria.

People with an indoor allergy can develop sinusitis because allergens can irritate the sinuses, in the same way that they irritate the lining of the nose. There is also a risk of secondary infection occurring because an excess amount of mucus or

nasal polyps
can stop the sinuses from draining properly.

Common symptoms of sinusitis include:

  • pain and tenderness of the infected sinus
  • a blocked or runny nose
  • a high temperature (fever) of 38C (100.4F) or above

Read more about

how sinusitis is treated


Immunotherapy carries a small but significant risk of triggering a serious allergic reaction, known as

. Symptoms of anaphylaxis include:

  • an itchy sensation in your throat
  • rapid swelling of your throat, mouth, lips and face
  • an itchy, red skin rash that quickly spreads across your body
  • increasing breathing difficulties due to swelling and tightening of your neck
  • a sudden intense feeling of apprehension and fear (which has been described as a "sense of impending doom")
  • a sharp and sudden drop in your blood pressure, which can make you feel light-headed and confused
  • unconsciousness

Anaphylaxis is a medical emergency that needs immediate treatment with a medication called adrenaline. Dial for an ambulance if you or someone you know experiences symptoms of anaphylaxis.

Due to the risk of anaphylaxis, immunotherapy should only be administered by a healthcare professional with the training and necessary equipment to treat it.

Read more information about immunotherapy and

how indoor allergies are treated

Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.