House dust mite and pet allergies occur because of a reaction to tiny airborne particles within the home. Symptoms can include a runny or blocked nose, itchy, red or watering eyes and wheezing. If you have asthma, your asthma symptoms can also be made worse by these allergies. Regular use of medication can improve symptoms but avoidance of the cause can also be important, especially with pet allergies.
What is the exact cause of house dust mite and pet allergies?
Tiny particles found in the air inside the home that cause allergic symptoms are called aero-allergens. These particles can include the poo (faeces) of house dust mites, and animal saliva, skin and urine. (Mould spores are another type of aero-allergen present in some homes, especially those with damp problems.)
Allergens are substances that cause an allergic response in certain sensitive people. They commonly cause problems with nasal, eye (ophthalmic) and breathing (respiratory) symptoms. These include inflammation of the nose (rhinitis), inflammation of the eyes (conjunctivitis) and wheezing. They can aggravate conditions such as asthma.
Aero-allergens rarely cause severe allergic reactions such as anaphylaxis. They are, however, some of the most common causes of allergies in general. See separate leaflet called Allergy - General Overview for more details.
Treatments do help improve symptoms. Avoidance of these allergens (or at least a reduction in their number) is also important.
How common are allergies to house dust mite and pets?
Allergies to house dust mite and pets are common. Also, in some countries, particularly in the developed world, atopic diseases affect up to 1 in 3 of the population. (Atopic diseases include asthma, eczema and hay fever.) About 1 in 2 adults with asthma, and about 8 in 10 children with asthma, have an allergic component to their disease.
What are the symptoms of house dust mite and pet allergy?
Symptoms of house dust mite and pet allergies include:
- Inflammation of the nose (rhinitis), causing runny nose or nasal congestion and sneezing.
- Inflammation of the eyes (conjunctivitis), leading to watering, itching and a hot feeling in the eyes.
- Wheezing, as such allergies can irritate the lungs. This may cause narrowing of the airways, leading to noisy breathing called wheezing. People with asthma frequently wheeze and allergies can cause the same symptom. People with asthma may wheeze more if they have allergies too.
- Other symptoms of house dust mite or pet allergies include:
House dust mite allergy
House dust mites are present in all homes in the UK. They are microscopic insects that live off human skin scales and form part of the dust in our homes. The climate and conditions inside our houses are ideal for their survival. They prefer bedrooms - in particular, beds and bedding. This is:
- Where we shed skin cells for them to feed on.
- Where we sweat, providing them with water
- Where the warmth sustains them and allows breeding.
The allergen that triggers the immune system and causes allergic problems is found mainly in the poo (faeces) of the house dust mites. These droppings are very dry, they break up (fragment) easily and the fine particles disperse into the air. The particles settle quickly into our pillows, mattresses, duvets, carpets and upholstery and are difficult to wipe out (eradicate). This means it is difficult to remove the source of the problem and prevent the allergic symptoms.
House dust mites are in all homes. It doesn't matter how clean and tidy you are. They affect homes regardless of lifestyle and income. Improvements in the way homes are insulated, including double glazing, has reduced air circulation and ventilation. As a result, moisture in the air (humidity) in homes has increased. This has made our homes a good environment for house dust mites to thrive.
Allergy to pets
Animal allergens are the second most common cause of allergic reactions. The allergens that trigger the allergic response are found in animal saliva, skin and urine. When animals groom themselves, they lick, and saliva coats the skin, fur or feathers. Skin cells covered in saliva are shed (this is called animal dander) along with loose hairs and fur.
Even so-called hairless breeds of cats and dogs can cause problems. Additionally, pets can have flaky skin complaints, like eczema, and so can spread large amounts of dander.
These allergen particles are microscopic, and so are easily airborne, and thus easily inhaled. This leads to typical respiratory symptoms, rhinitis and allergic conjunctivitis.
Pet cats are the most problematic animal in terms of allergen production, due to their behaviour of frequent grooming. Dogs come second but any animal can be a cause of an allergic reaction. Parrots and other birds are another cause of allergic reactions to their feathers. In small animals, such as mice, gerbils and guinea pigs, it is the urine that is the most potent allergen. This means that the animal cage and bedding are heavily contaminated with allergen. When the urine dries, and the bedding is disturbed (either by animal movement or by cage cleaning), allergen is released into the air.
Do I need any tests?
Many people with pet allergy do not need any tests as the cause of the allergy is clear. Symptoms are worse in the home where the pet is. Symptoms improve when out of the home, especially for longer periods, such as on holiday. Some people with asthma are advised to avoid contact with pets if it makes their symptoms worse, or to try to reduce house dust mite if symptoms are severe or difficult to treat.
If required, both house dust mite and pet allergy can be diagnosed with skin prick tests. This is usually done in a hospital by either an allergy specialist, an immunologist or perhaps a skin specialist (dermatologist).
What are the treatment options?
Some general points
- Cigarette smoke makes all allergic conditions worse. It aggravates already inflamed skin and membranes in the nose, windpipe and lungs (the respiratory tract). Nobody should smoke in the home of an allergy sufferer.
- Babies exposed early on to allergens and smoke are more likely to develop allergic diseases.
- Allergic symptoms to aero-allergens can develop over time. Therefore, once you have identified the problem, and taken steps to reduce the burden of allergens, it can take some time for symptoms to improve.
- The best treatment is ultimately allergen avoidance. This needs to be rigorously and consistently followed in order to achieve symptom relief over a long period of time. However this can be difficult and is not always possible or practical.
Treatment with nasal sprays, eye drops and/or antihistamine tablets will often ease or clear the symptoms. The treatment is the same as for any cause of allergic rhinitis or allergic conjunctivitis.
Avoiding the cause of the allergy
Treatment with medication often works so well that you may not have much motivation or need to avoid the cause of the allergy. However, some people may wish to try to avoid the cause of the allergy, particularly if medication is not fully effective.
Avoidance of house dust mite
If house dust mite is the cause of the allergy, it is impossible to keep your home permanently clear of the mites and their droppings. However, the following will help to reduce their number greatly, which may ease symptoms. The main focus is on the bedroom:
- Remove carpets and rugs (where possible) from the bedroom. Hard floors such as wood are preferable. Avoid soft furnishings in the bedroom.
- Use dust-tight (mite-proof) covers for mattresses, duvets, and pillows. These can be left in place for several months. The usual covers and cases can be put on top of the special covers, but should be washed every 1-2 weeks at 60°C. However, on their own, such covers are not likely to be effective.
- Use feather rather than synthetic pillows (this is the opposite to what used to be thought).
- Wet-dust the bedroom furniture every week.
- Vacuum or clean the bedroom floor regularly. Use a vacuum cleaner with a good filter (this removes the mite and prevents small particles coming out through the vacuum exhaust). Domestic steam carpet cleaners have no effect on house dust mite populations. Indeed, increasing the moisture content of the carpet can increase numbers. However, high temperature professional steam cleaning can kill the mites and stop the droppings from causing allergic problems.
- Regularly ventilate the bedroom (open the door and a window for a while on most days).
- Keep soft toys to a minimum. Put them in the freezer, in a plastic bag, for 24 hours now and again. This kills any mites on them. If the toys are washable, wash them at 60°C after putting them in the freezer.
- Try to keep moisture in the air (humidity) low (for example, do not dry washing on the radiators).
- Let bedding air after use (that is, fold back duvet or blankets to allow sheets to air and sweat to evaporate).
- Chemical treatments (acaricides) can be used to kill the mites. However, treatments are only recommended for carpets. There are certain drawbacks that include the time taken to apply the products properly, and their effectiveness. It is possible that carpets can be stained and that inhaling these products during application may be harmful.
Symptoms of house dust mite allergy may also improve when on holiday in warm dry climates where there are fewer mites.
Reducing the impact of pet allergy
With allergies to domestic pets, the main strategies for minimising allergic problems and aero-allergens are to:
- Avoid getting any new pets.
- Confine existing pets to defined areas of the home.
- Remove carpets and rugs, if possible, from the rooms where pets are kept.
- Ensure pets are not allowed into the bedrooms.
- Wash dogs (and cats, if possible), regularly!
- Groom animals regularly outside, to remove hairs.
- Clean surfaces, including walls, regularly.
- Vacuum regularly, if possible with a vacuum cleaner that has a good filter.
- Wash pet bedding frequently.
- Not allow pets to lick your hands or face.
- Consider, in extreme circumstances, that it may be necessary to re-home your pet.
This treatment is sometimes used, mainly in cases that are severe and where symptoms are not helped much by other treatments.
It is done using a series of injections to desensitise the immune system. The allergen you are allergic to is administered in tiny quantities, via an injection. The amount used is so small that it only very rarely causes the allergic reaction, but is enough to teach the immune system not to react. Increasing doses of allergen are given at regular intervals (usually weeks to months).
Immunotherapy is time-consuming and expensive, and it carries a degree of risk. For this reason, it needs to be carefully supervised by a specialist, and performed in a hospital outpatient setting. It would only be tried if other methods had previously failed.
A newer technique involves placing the allergen under the tongue (drops or tablets). This type of immunotherapy is increasingly being used in allergy clinics; however, it is still not widely available. Often, long-term treatment (up to three years) is needed for this under-the-tongue (sublingual) method.
Dr Katrina Ford
Dr Roger Henderson
Prof Cathy Jackson