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What is the difference between demodex, dust mites, bed bugs and scabies?


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There is a difference between dust mitesdemodex, scabies, and bed bugs . So what are the differences?

While morphologically they are different we are concentating on the size in this post. Many may be confused about these four critters, so here are some facts: 


Dust mite image courtesy of Wikimedia Commons -

 Dermatophagoides farinae measures 0.2–0.3 mm (0.008–0.012 in) in length difficult to see with the naked eye

Demodex Image courtesy of Wikimedia Commons

adult, D. folliculorum can measure 0.3–0.4 mm (0.012–0.016 in) in length and possess four pairs of short legs near its head and neck region, so they are are barely seen with naked eye. 

Scabies (Sarcoptes scabiei) Image courtesy of Wikimedia Commons

- Females are 0.3–0.45 mm (0.012–0.018 in) long and 0.25–0.35 mm (0.0098–0.0138 in) wide, and males are just over half that size and may appear as tiny black dots to the naked eye

Bed Bug Image courtesy of Wikimedia Commons

 - Adults grow to 4–5 mm (0.16–0.20 in) long and 1.5–3 mm (0.059–0.118 in) wide, so they can be seen easily with the naked eye. 

1 Centimeter (cm) = 10 Millimeters (mm) 

1 centimeter = 0.393701 inch
1 inch = 2.54 centimeters

1 millimeter is 10 times smaller than a centimeter.
1 millimeter (mm) = 1000 micrometers (μm)

images courtesy Wikimedia Commons

0.3 mm = Grain of Salt
  1 mm = One sheet of paper
1.5 mm = Diameter of pin head
10 mm = Ten sheets of paper

A micrometer (symbol, μm - also called a micron) is 1000 times smaller than a millimeter ( or one millionth of a metre). 

Average Size of Demodex Compared with Dust Mite or Bed Bug
"Using a confocal laser scanning in vivo microscope allowed determining the average size of Demodex mites. When determining the size of mites from 100 to 200 μm, it was believed that in this case Demodex brevis was observed, while the average length of the mite was 125 μm; from 200 to 400 μm – Demodex folliculorum with an average length of 293 μm. The average size of the width of Demodex mites was 24 μm." [1]

Wikipedia reports that the d. folliculorum measures 0.3 - 0.4 mm which is an average of 0.35 mm. The Russian study mentioned in end note 1 reports the average length of 293 μm which is 0.293 mm, about the length of a grain of salt, but of course, thinner in width.  

So the demodex you can barely see with the naked eye (a microscope or dermoscopy facilitates an investigation better than the naked eye). The dust mite is more difficult to see with your naked eye and is barely smaller in size to the average demodex mite. The bed bug you can easily see with your naked eye and is the largest of the three critters.  There is an article discussing dust mites and atopic dermatitis [2]. The scabies (Sarcoptes scabiei) mite may look like tiny black dots to the naked eye. [3]

Better Viewing Demodex with a Microscope or Dermoscopy
A cheap microscope can view demodex a lot better than using your naked eye. Dermatologist sometime use both a microscope in their office but usually use dermoscopy in their office exam of a patient. You too can purchase either device and view these critters yourself. 

Dermoscopy is using a device similar to the one below available at Amazon:

3GEN DL1 Epiluminescence Dermlite Dermatoscope

Skiary Smartphone Dermatoscope

Confocal Laser Scanning in Vivo Microscopy
A Russian study concluded that the Confocal laser scanning in vivo microscopy was superior to using a skin scraping with a light microscope. [4]


Decreasing Demodex Density Count Improves Rosacea

Why do demodex mites like human skin?

Ward's Demodex in Situ Slide

So you should differentiate whether you are suffering from either demodex, dust mites, bed bugs or scabies. A dermatologist can determine if you are suffering from either one of these critters. All mite afflictions are treatable and respond well to treatment. 

In this forum rashes from bed bugs (are not a mite, are instead insects in the family Cimicidae) or dust mites are rarely mentioned, while scabies is rarely mentioned (except in this post and so far one other) and if you do have a rash from any of these (except demodex), you may be suffering from Atopic Dermatitis.  Demodex mites are involved with demodectic rosacea

However, many have reported success treating demodectic rosacea with Soolantra, horse paste, the ZZ cream, Cliradex, OvanteUngex, and a number of other treatments

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End Notes

[1] Dermatol Reports. 2019 Jan 23; 11(1): 7675.
Clinical picture, diagnosis and treatment of rosacea, complicated by Demodex mites
Alexey Kubanov, Yuliya Gallyamova, and Anzhela Kravchenko

[2] Vitamin D, Dust Mites, and Atopic Dermatitis
Korean study suggests a connection, Medpage Today

[3] CDC, Biology, Parasites, Scabies 

Scabies Slideshow: Symptoms, Cause, and Treatments, WebMD

Crotamiton, a prescription drug used to treat scabies has been reported to improve rosacea. 

[4] Russian Study on Demodex Mites and Rosacea Illuminating

Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser confocal scanning microscopy (LCSM), Wikipedia

How does a confocal microscope work?, Emory University 


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