Dust mites are arthropod insects that are close relatives of spiders and flat ticks (also called ticks and grass crawlers) in terms of biological classification.
However, they have different habits than spiders or ticks, preferring warm, humid environments and living with humans because the dander shed by human skin is their favorite food, and of course the dander and hair shed by small, hairy animals is also a good treat. Dust mites live with humans every day and are harmless to most people, but for those who are allergic to dust mites, it is no small problem. Today, let’s learn more about dust mites and the allergies caused by them.
What kind of insects are dust mites?
1. Adult dust mites are about 0.5mm in length and cannot be seen with the naked eye;
2. Adult dust mites have a maximum life span of 3 months;
3. The female dust mite lays 1-2 eggs per day;
4. Dust mites prefer a dark, humid and warm environment;
5. Dust mites that cause allergies are mainly house dust mites and dust mites, and in the south of China there are also tropical clawless mites.
Where do dust mites like to hide?
The human home is the home of dust mites, and they like to hide in dusty, food-rich places: mattresses, bedding and pillows are full of shed dander, which is their favorite place. According to research, the number of dust mites per bed is more than 2 million.
Carpets, curtains, upholstered furniture (fabric sofas, etc.), various ornaments and air conditioning filters easily accumulate dust and are also good hiding places. The number of dust mites on the surface of a new or long-used summer mat, or on an air conditioning filter that is not cleaned for 7 days, exceeds ten thousand.
Plush toys are the favorite of children, but also the favorite of dust mites, and when children hold plush toys Happy every day is the moment when dust mites start a delicious meal. Small dogs and cats are the best mobile homes for dust mites, living in their dense fur and enjoying their meals on the move at any time.
Of course every warm, humid corner of the house is good too. As long as the temperature exceeds 25°C and the humidity exceeds 60%, dust mite mothers will be busy raising their offspring, so the warm, humid summer months are the dust mites’ favorite season. Besides home, some public places such as cinemas, baths, hairdressing salons and libraries are also places where dust mites gather in large numbers.
How do dust mites cause allergic reactions?
Dust mites do not bite, and for people who are not allergic to dust mites, this tiny bug is not harmful. Dust mites cause allergies mainly from dust mite excrement (feces) and shed skin crusts. Scientists have found that there are more than twenty components in the material excreted or shed by dust mites, each of which can cause allergic reactions in humans. Because the material shed by dust mites is so tiny and often suspended in the air, it is more likely to cause respiratory allergic reactions such as allergic rhinitis and asthma. Dust mites also cause eye irritation (allergic conjunctivitis) with itchy, red and watery eyes. Of course, dust mite allergens suspended in the air can also cause eczema to worsen when they adhere to the skin of allergy sufferers.
How is dust mite allergy determined?
Dust mite allergy causes the body to produce an antibody, IgE, which is the main cause of allergic symptoms in various organs of the body. Therefore, testing the body for dust mite IgE can help us determine if we have a dust mite allergy. The two most used methods are the skin prick test and the blood test for IgE antibodies.
Skin prick test: Put a drop of dust mite allergen extract on the skin of the forearm, gently prick the skin with a prick needle to the extent that it does not bleed, let the allergen extract slowly penetrate into the dermis, and observe the result after 15-20 minutes, expressed as a positive reaction level (1+~ 4+). This method can determine the presence of dust mite IgE antibodies in the skin.
TIPS: The advantages of this test are that it is inexpensive, quick, may be mildly painful, and can be tolerated by most children or infants. However, the test results are affected by some oral medications or topical medications, or by the examiner’s practice, and often have false-positive or false-negative results. Blood sampling for IgE: 3-5 ml of peripheral blood is taken intravenously and sent to the laboratory for testing. The test methods are RAST method, ImmunoCap method, ELISA method, immunoblotting method, etc. The test results are expressed as level 1~6, and there may be a difference of 1 level between the test results of different methods. This method can determine the presence of dust mite IgE antibodies in the blood.
TIPS: This test is more expensive and takes a little longer, but the specificity is better and the test results are not affected by the medication taken.
Does the presence of dust mite IgE antibodies in the blood or skin necessarily mean that I will develop dust mite allergy symptoms? Not necessarily. There are some patients who test positive for dust mite allergens but do not experience symptoms such as sneezing, runny nose, wheezing or itchy eyes in a dusty environment with high dust mite concentrations. This is mainly because any test can have a false positive or false negative result, or the IgE antibody level is very low and not sufficient to cause symptoms of allergy. Therefore, the results of the allergen test have to be analyzed in conjunction with the symptoms that occur with exposure to dust mites, or after a period of follow-up and repeat testing to determine if there is a dust mite allergy. How do dust mites cause exacerbation of eczema?
Patients with atopic dermatitis/eczema are often tested for allergens, such as skin prick tests or blood tests for IgE antibodies, and roughly 30-70% of eczema patients are found to be positive for dust mites.
But are dust mites necessarily the cause of eczema exacerbation?
The common clinical method of allergen screening we described earlier is to identify dust mite allergy by checking for IgE antibodies in the skin or blood. IgE antibodies are the main cause of lung or nasal allergy from dust mite allergens, while for skin allergic reactions, IgE antibodies are only partially responsible for dust mite induced eczema. There are more than 20 components of dust mite allergens, some of which can directly damage the skin structure and cause skin inflammation, when it is not related to IgE antibodies. We can also determine whether dust mites cause exacerbation of eczema by a skin patch test. The prepared dust mite allergen extract is applied directly to the back skin for 48 hours and then removed. Some patients with atopic dermatitis/eczema will show eczema in the area where the dust mite allergen was applied, which will prove that dust mites directly cause eczema exacerbation. As illustrated below.
However, this method is not currently used in clinical routine testing and is only used when doing scientific research. It was found that patients with eczema exacerbated by dust mite allergens were more likely to have rashes on the face, neck and distal extremities because dust mite allergens are usually suspended in the air and exposed skin is more likely to be contaminated with the allergens, thus triggering allergic skin inflammation. It was also found that patients with positive IgE antibodies to atopic dermatitis/eczema did not always have positive skin patch tests for dust mite antigens because the IgE antibodies detected in these patients were mainly associated with their coexisting rhinitis or asthma and not directly related to eczema.
Therefore, patients with atopic dermatitis/eczema who test positive for dust mites through skin prick tests or blood tests for IgE antibodies should always take a medical history and perform a dust mite allergen patch test to determine if dust mites are responsible for exacerbating their eczema.