Testing for Demodex

Testing for Demodex is not commonly performed in human medicine. We hope that will change in order that more targeted treatment can be given. Where confirmation is required, due to uncertainty over clinical signs, the following tests can be done quickly and with minimal resources:

• In eyelashes: Slit lamp examination: Colarettes and dandruff in the eyelashes are a giveaway sign of Demodex presence. Sit your patient at the slit lamp and ask them to look down. Use 12-16x magnifification to view the eyelash margin clearly. Remember that Demodex can be found in clean lashes too, so the next step could be ‘Lateral Eyelash Tension’: This requires just the slit lamp and good tweezers – see how here: Müntz Video 1, Müntz Video 2. This technique avoids pulling out eyelashes and is not uncomfortable for the patient¹.

• In the skin: A comedone extractor can be used to expel and collect the contents of blocked pores for microscopy. Start with 45 X. Standardised skin surface biopsy (SSSB) requires ‘Superglue’ and a standard light microscope – see how here: Forton Video ².

• Skin scrapes are done on inflamed skin by putting mineral oil on the affected area then scraping it with a blunted blade to collect the debris for microscopy. Some authors advocate squeezing the area to the extent that some bleeding may occur³. This is more important for Demodex, which live deeper than some other ectoparasites such as scabies. Clear instructions can be found in some veterinary sources⁴. Use of dark field microscopy helps visualisation as living Demodex are bioluminescent⁵.

PCR: Digital polymerase chain reaction, based on the 18s ribosomal RNA (18s rRNA) gene, may also be used to detect Demodex in Demodex blepharitis and presumably in many other tissue or fluid samples. However, be aware that some of the other ectoparasites which may affect humans could be missed if the corresponding primer for that species is not used. Some of the thousands of ectoparasites which could potentially be picked up from pets, wildlife and farming, are listed on this site⁶.

Please see the supplementary ‘Data Sheet‘ no. 1 on our Frontiers 2025 paper for more information and associated references.

1. Zhang, AC, Müntz, A, Wang, MTM, Craig, JP, & Downie, LE. Ocular Demodex: a systematic review of the clinical literature. Ophthalmic Physiol Opt 2020; 40: 389– 432. Doi: 10.1111/opo.12691
   doi.org/10.1111/opo.12691 ↩︎
2. Forton FMN & De Maertelaer V. Two consecutive standardized skin surface biopsies: An improved sampling method to evaluate demodex density as a diagnostic tool for rosacea and demodicosis. Acta Dermato-Venereologica.2017; 97(2): 242–248. doi.org/10.2340/00015555-2528 ↩︎
3. Foley R, Kelly P, Gatault S, Powell F. Demodex: a skin resident in man and his best friend. J Eur Acad Dermatol Venereol. 2021;35(1):62-72 doi.org/10.1111/jdv.16461 ↩︎
4. Skin scraping for external parasites. Deboer DJ. A clinician’s guide to dermatology (Ebook) 2026 Link Here ↩︎
5. Aytekin S, Yaşar S, Göktay F, Güneş P. Spontaneous fluorescence of Demodex in the dark. (letter) JEADV 2016, 30, 320–38. doi:10.1111/jdv.12776
   Link Here ↩︎
6. Kasetsuwan N, Kositphipat K, Busayarat M, Threekhan P,Preativatanyou K, Phumee A, Siriyasatien P. Prevalence of ocular demodicosis among patients at Tertiary Care Center, Bangkok, Thailand. Int J Ophthalmol. 2017;10(1):122-127. Published 2017 Jan 18. doi:10.18240/ijo.2017.01.20
   https://www.ncbi.nlm.nih.gov ↩︎