Human Demodicosis: Revisit and a Proposed Classification

W. Chen; G. Plewig


The British Journal of Dermatology. 2014;170(6):1219-1225. 

In This Article

Terminology of Demodicosis

The current terminology to describe human demodicosis is unspecific and confusing, and may include pityriasis folliculorum,[30,33] rosacea-like (rosaceiform) dermatitis,[16,17] demodectic rosacea,[34] Demodex facial dermatitis,[35] granulomatous rosacea-like dermatitis,[33] perioral/periorbital dermatitis-like demodicosis,[3,33] facial demodicosis,[36] pityriasis folliculitis,[37] scalp folliculitis,[38,39] favus-like scalp demodicidosis,[40]Demodex abscess[41] and facial abscess-like conglomerates.[42] We propose the following classification to describe primary demodicosis ( Table 2 ).

Spinulate demodicosis, currently known as pityriasis folliculorum, describes discrete, fine, whitish, partly yellowish, spiky changes involving mainly facial sebaceous hair follicles, which are isolated but grouped, with or without faint erythema and little inflammation (Figure 1). It is likely caused by the caudal portion of the mites (opisthosoma of Demodex).

Figure 1.

Spinulate demodicosis. Primary human demodicosis depicting discrete, fine, whitish, partly yellowish, keratotic, spiky scaly changes involving sebaceous hair follicles in the background of faint erythema.

Demodex folliculitis, meaning inflammation of the follicle due to Demodex mites, can be morphologically divided into the following patterns: papulopustular (Figures 2 and 3), nodulocystic (Figure 4) and conglobate, which depicts abscess-like lesions. Perioral demodicosis is a primary demodicosis and should be differentiated from perioral dermatitis with a secondary increase in Demodex mites. The use of 'perioral dermatitis-like demodicosis' is confusing and superfluous. According to the morphological pattern and localization, it may be termed 'papulopustular perioral demodicosis' or 'papulopustular periorbital demodicosis'. Demodicosis of the scalp (demodicosis capitis) occurs more commonly on the balding scalp of elderly men,[38,39] who rarely develop bacterial folliculitis (personal observation). Crusted demodicosis with thick yellow crusts is associated with chronic long-standing inflammation caused by Demodex mites (Figure 5).

Figure 2.

Papulopustular demodicosis. (a) Primary human demodicosis characterized by a typical protracting course involving the forehead of a 46-year-old man with agminated follicle-bound lesions in an irregular shape. (b) Microscopic examination of skin scrapings revealed more than 5 mites per cm2.

Figure 3.

Papulopustular demodicosis. Primary human demodicosis displaying disseminate involvement of the face of a 64-year-old woman with mild keratotic inflammatory papules of different sizes in an asymmetric distribution.

Figure 4.

Nodulocystic demodicosis. Primary human demodicosis with intense inflammatory reaction including pus and suppurative succulent changes.

Figure 5.

Crusted demodicosis of the face. Primary human demodicosis showing multiple partly confluent papulopustules with thick yellowish crusts.

Ocular demodicosis may include blepharitis or chalazia due to Demodex and, less commonly, conjunctivitis due to Demodex.[43,44]

Auricular demodicosis involves the external ear canal or tympanic membrane (myringitis due to Demodex).[45]