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.
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:
- Demodex folliculorum – rough skin due to increased scale within hair follicles
- Rosacea, particularly asymmetrical papulopustular or granulomatous variants
- Some cases of perioral dermatitis
- Blepharitis (inflammation of the eyelid margins)
Demodex folliculorum is also known as pityriasis folliculorum. It is a form of digitate keratosis.
How is demodex found?
Demodex folliculorum is characterised histologically by:
- Numerous demodex mites in the infundibula of the follicles (> 5/cm2
- Follicular hyperkeratosis
- Focal follicular lichenoid lymphocytic infiltrate
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:
- Using mild shampoo on hair and eye lashes every day
- Cleansing the face twice daily with a non-soap cleanser
- Avoiding oil-based cleansers and greasy makeup
- Exfoliate periodically to remove dead skin cells
If demodex infestation is heavy, the mites may be temporarily eradicated with topical insecticides, especially:
- Crotamiton cream
- Permethrin cream
- Ivermectin cream or tablets
In severe cases, such as those with HIV infection, oral ivermectin may be recommended.
- Book: Textbook of Dermatology. Ed Rook A, Wilkinson DS, Ebling FJB, Champion RH, Burton JL. Fourth edition. Blackwell Scientific Publications.
- Forton F, Germaux MA, Brasseur T, De Liever A, Laporte M, Mathys C, Sass U, Stene JJ, Thibaut S, Tytgat M, Seys B. Demodicosis and rosacea: epidemiology and significance in daily dermatologic practice. J Am Acad Dermatol. 2005 Jan;52(1):74-87. Medline.
On DermNet NZ:
- Demodicosis – Medscape Reference
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