Demodex: Exploring Its Role in Rosacea

With increased understanding of the human microbiome, physicians and especially dermatologists are considering its affects on health. In particular, there has been increased focus on the potential role of Demodex mites in rosacea. The National Rosacea Society recently convened a roundtable discussion, with support from Galderma, to bring together experts to discuss the role of Demodex in rosacea.

Although Demodex mites are a normal part of the human microbiome, they have been found in more than four times greater numbers on the facial skin of rosacea sufferers, according to Dr. Frank Powell, consultant dermatologist at Mater Misericordiae Hospital in Dublin and former president of the European Academy of Dermatology and Venereology. Ahead, Dr. Powell answers questions about Demodex and rosacea.

Figure. The microscopic skin mite Demodex folliculorum. Courtesy NRS.

As new research is emerging, how would you best describe the role of Demodex in rosacea?

“The role of Demodex in rosacea is unclear. It is not solely the cause,” Dr. Powell says. But he adds, “It probably is a factor in some patients.”

Demodex folliculorum and D. brevis have long been known to live in the hair follicles and sebaceous glands of the facial skin. D. folliculorum is also found in the meibomian glands of ocular rosacea patients.

Dr. Powell has suggested that a genetic predisposition for rosacea may be reflected in a different skin type with specific lipid qualities that allows Demodex to flourish in greater numbers. The finding that individuals who had significant acne when younger often are observed to have rosacea later may supports a possible genetic component in patients with skin that reacts to either Propionibacterium acnes or Demodex.

During the roundtable, discussion touched on the fact that microbic organisms that live on Demodex mites may also be involved in rosacea. A recent study found a diversity of such microorganisms, including a total of 92 species, 36 of which were never before recorded on humans.

Do you discuss Demodex with patients? If so, what do you say?

“I do discuss Demodex with patients,” Dr. Powell says. They should understand that rosacea is not caused by an infection. “I tell them that we all have these mites but that patients with rosacea have more than average,” he says.

In the roundtable, you mentioned a Super Glue test for Demodex. Is this a potential clinical tool?

“The glue is put on a glass slide that is placed on the skin. The glue dries and when the slide is removed it extracts the contents of the follicles in which the Demodex lives,” Dr. Powell, explains.“It is mainly used for researchers or by dermatologists who feel a particular case is abnormal,” he adds.

Now that a topical ivermectin formulation that targets Demodex is available in the US for rosacea, where do you think it fits in the treatment regimen?

Ivermectin is a known anti-vermicidal and antiparasitic recently shown to have anti-inflammatory actions, as well. In a large study on the action of topical ivermectin in patients with moderate to severe rosacea, 38.4 to 40.1 percent of subjects received physician assessments of clear or almost clear. At 12 weeks, there were 64.9 to 65.7 percent mean reductions of inflammatory lesions of test subjects.

“Topical ivermectin is establishing itself as an alternative mainstream treatment to more established treatments of metronidazole and azelaic acid,” per Dr. Powell. n