All you need to know about the house dust mite
Dust Mite Studies

Eczema and the house dust mite (HDM)

Excessive exposure to house dust mites (HDM) can cause allergic rhinitis, asthma and eczema. In order to reduce exposure, doctors say it is essential to understand the how mites live and why they cause disease. Below are some simple facts about the mite and practical advice on how to keep beds and bedding mite free.
House Dust Mites (HDM)

House dust mites are tiny scavengers that live in colonies in dark, damp, warm, and still environments like carpet, sofas, beds and bedding. They eat a wide-range of organic debris including pollens, cotton fibre, dead insects, fungi or grain, but their favourite food consists of discarded old skin scales covered in bacteria, yeasts, fungi and micro-organisms.

Adult mites are blind, take in water and oxygen through their shell-like covering, and can produce up to 20 droppings a day. The droppings are water-soluble and light enough to be pushed into the air by disturbance where they can be breathed in or be deposited into eyes or on skin.

Importantly, the mite has no stomach but a chambered gut that produces powerful digestive enzymes designed to break down the wide-range of food that the mite eats. Both leftover hard-to-digest food, and the powerful enzymes can be found in mite droppings.

One of these enzymes is a major cause of allergy, because it can melt the glue that binds delicate cells together, killing the cells and creating a breach in the cell defences. The delicate cells at risk include those in the nose, lungs, or on vulnerable skin prone to eczema.

The life span of a single successful HDM is about three months. It measures approximately a third of a millimetre in length, is up to 75% water and, because of water transparency and size, is barely visible to the human eye.

A single travelling mite rarely survives, but a colony travelling on a vehicle such as second hand furniture, a pillow, sweater or blanket can travel the globe if the conditions are right.


Eczema

Eczema is described as a chronic, inflammatory, itchy skin condition that usually develops in early childhood and has a genetic link that often makes the skin barrier work less well. Chronic dry skin is a symptom of a flaw in the building blocks of the skin barrier. This leads to water loss causing dry skin.

A poorly working skin barrier can be made worse by things like irritants, allergens, infections, and changes in the weather. In eczema exposure to the enzymatic droppings from HDMs can act as both irritant, or allergen (resulting in a flare-up) and cause a breach in skin defences inviting bacterial infection to become established.

In order to combat the mite it is essential to understand a mites way of life and why it can cause allergic disease. We must also learn to recognise those who are vulnerable and at risk from mite exposure. This group includes young children born with dry skin and those who are sensitive or allergic to house dust mites.

Chronic itching, sneezing, coughing and wheezing, especially in children, are common telltale symptoms of allergy. Symptoms that young children may think are normal in growing up.

Tests completed on people with atopic dermatitis (eczema) demonstrate that a reduction of mite allergens improved the condition, greatly reducing the activity of atopic dermatitis in some people. There is a need to identify the people who would gain from this intervention.

P.S.Friedman, The Lancet, 347, 6th January 1996


The presence of house dust mites and their active digestive enzymes in a mattress, on sheets, in pillows or duvets is a risk factor in eczema. There are over 23 known and separate allergens from house dust mites, most of them are enzymes.


Keeping Mites Out of Beds

The simple steps below will show how to make a bed mite free. They are based on successful clinical trials in house dust mite avoidance.

  1. Place a tightly woven, anti-mite, micro-porous cover on a clean mattress. Make sure the mattress is completely enclosed and the cover has been clinically tested and medically approved.
  2. Place a heavy cotton quilted cover over the micro-porous cover to absorb perspiration and collect discarded skin scales and dust.
  3. Put micro-porous covers on duvets and pillows, as these can be a home for house dust mites as well.
  4. Hot wash all bed linen weekly. The quilted cover only needs to be hot washed every two weeks, but it must be completely dried before being put back on the bed.
  5. While the quilted cover is off the bed, damp wipe the micro-porous cover to prevent a build-up of dust or skin scales.

Nightwear should be made of cotton to absorb perspiration, skin scales and dust. Soft toys that go into beds with small children should be hot washed weekly.


Statistics show that there is a greater incidence of allergic eczema before the age of seven with prevalence for the disease running at 10-12% of the populations. Manifestations of eczema are higher in families with a history of allergy. In those children affected 10 to 20% of these will continue to have eczema into late childhood. From this group it is estimated that 10 to 15% will experience persistent eczema in life.

The medical history of the disease

1892 It was first described in its clinical form by Besnier as an itching skin disorder associated with a family history of the disease, often starting in infancy and associated with asthma and hay fever. The disease took a chronic and fluctuating course with seasonal variations.

In 1902 the famous statement, still used today, describes the condition, 'It was not the eruption that itched but the itch that erupted'.

In 1923 the term atopy was first used to describe allergy in its clinical form. 'allergic reaction to a substance in the environment'.

In 1933 atopic dermatitis (eczema) was included in the group of allergic diseases. It was described then as, inherited and chronic weeping or dry skin conditions that is seen in childhood and adults.


References

'House dust mites in atopic dermatitis', Penny Fitzharris, Greta Riley, 'International Journal of Dermatology', 1999, 38; 173-175