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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Demodex

What is demodex?

Demodex is the name given to tiny mites that live in the hair follicle. In humans, demodex is found on facial skin especially the forehead, cheeks, sides of the nose, eyelashes and external ear canals. The condition it causes is called demodicosis.

There are two mites principally involved in human demodex infestations, Demodex folliculorum and Demodex brevis. D folliculorum is found in small hair follicles, particularly the eyelashes. In both its immature and adult stages it feeds on skin cells. D. brevis is found in the oil glands that are connected to small hair follicles and feeds on the gland cells.

D. folliculorum mites are 0.3-0.4mm in length and D. brevis 0.15-0.2mm. This makes them invisible to the naked eye but under the microscope their structure is clearly visible. The 8 legs of this mite move at a rate of 8-16 mm/h and this is mainly done during the night as bright light causes the mite to recede back into the follicle.

Who has demodicosis?

Human demodex mites are found mostly on older children and adults and rarely in children under 5 years old.

The mites may proliferate in immunodeficiency states such as human immunodeficiency virus (HIV) infection.

What are the clinical features of demodicosis?

Patients with demodicosis may have eye irritation, itching and scaling of eyelids (eyelid dermatitis). There may be lid thickening, loss of lashes, conjunctival inflammation and decreased vision.

It has not yet been established if demodex is responsible for any skin diseases but increased numbers of demodex mites have been observed in the following conditions:

How is demodex found?

Demodex may be found in mineral oil skin scrapings from the face by KOH examination, or in a skin biopsy examined under the microscope.

What is the treatment for demodicosis?

Demodex can only live in the human hair follicle and when kept in check they cause no problems. Thus treatment is aimed at trying to control proliferation of demodex mites. Many treatments involve spreading an ointment at the base of the eyelashes at night to trap mites as they emerge from their burrow and move from one hair follicle to another.

A current popular treatment is to firstly debride the lashes and lash roots with scrubs and then treat the area with tea tree oil and Macadamia nut oil to try and kill any eggs. This treatment is usually performed at the doctor’s rooms. Other treatments include scrubbing the affected area with mercury oxide ointment, baby shampoo or rubbing alcohol.

Home treatment and prevention strategies include:

If demodex infestation is heavy, the mites may be temporarily eradicated with topical insecticides, especially:

Topical erythromycin or metronidazole may also be used to treat eye infections involving the lids, conjunctiva, and/or cornea.

In severe cases, such as those with HIV infection, oral ivermectin may be recommended.

Related information

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Author: Vanessa Ngan, staff writer.

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If you have any concerns with your skin or its treatment, see a dermatologist for advice.