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.

Human demodex mites may be found on most older children and adults but is rare in children under 5 years old. The mites may proliferate in immune deficiency states such as human immunodeficiency virus (HIV) infection.

Describe demodex

There are two mites principally involved, Demodex folliculorum and Demodex brevis. D folliculorum is found in small hair follicles, particularly 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.

Does demodex cause skin problems?

It has not yet been established if demodex is responsible for any skin disease (demodicosis). Increased numbers of demodex mites have been observed in the following conditions:

• ‘Pityriasis folliculorum’ – rough, dry and scaly skin
• Rosacea, particularly asymmetrical papulopustular or granulomatous variants
• Some cases of perioral dermatitis
• Blepharitis (inflammation of the eyelid margins)

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.

Should demodex be treated?

Demodex can only live in the human hair follicle and when kept in check cause no problems. However, to reduce the chance of the mites proliferating excessively:

• Cleanse the face twice daily with a non-soap cleanser
• Avoid oil-based cleansers and greasy makeup
• Exfoliate periodically to remove dead skin cells

If your doctor thinks your skin condition may be related to demodex, the mites may be temporarily eradicated with topical insecticides, especially:

• Crotamiton cream
• Permethrin cream

Metronidazole gel or orally may also clear demodicosis.

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