Thursday, August 30, 2012

Rosacea - What Causes It? News story overplays suggested connection to skin mites

Just got done reading this: Could Bacteria in Skin Mites Help Cause Rosacea? - US News and World Report.  The article leads off with a bold statement that caught my eye
"Bacteria carried by tiny mites on the skin might be responsible for the common dermatological condition known as rosacea, researchers say."
This caught my attention because I have been reading up on skin microbes recently and though many have suggested connections between microbes and rosacea as far as I know nobody has shown any causal relationship.  And causation vs. correlation has been on my mind a lot recently.

So I read further and found some suggestive but inconclusive statements that were linked together
  • there are more of these mites on the skin of patients with rosacea than on those without
  • a bacterium (Bacillus oleronius) has been found in the mites and in people w/ rosacea
  • this bacterium can be killed with the same antibiotics that seem to have some success in treating rosacea
  • people with rosacea have an immune reaction to compounds from this bacterium 
  • another bacterium Staphylococcus epidermis also appears in patients w/ rosacea but not patients free of rosacea
And that apparently was it ... not very convincing.  Sounds like just a lot of random correlations to me.  So I decided to dig deeper.  And I went to see fi I could find the paper which alas was not linked from the news story.

I googled the journal name "Journal of Medical Microbiology" and got to the web site.  The news article had said the "review paper" had come out August 30th so I clicked on the Papers In Press link and got to the paper.  I browsed the abstract, which seemed somewhat different from the gist of the news story

Rosacea is a common dermatological condition that predominantly affects the central regions of the face. Rosacea affects up to 3% of the world’s population and a number of subtypes are recognized. Rosacea can be treated with a variety of antibiotics (e.g. tetracycline or metronidazole) yet no role for bacteria or microbes in its aetiology has been conclusively established. The density of Demodex mites in the skin of rosacea patients is higher than in controls, suggesting a possible role for these mites in the induction of this condition. In addition, Bacillus oleronius, known to be sensitive to the antibiotics used to treat rosacea, has been isolated from a Demodex mite from a patient with papulopustular rosacea and a potential role for this bacterium in the induction of rosacea has been proposed. Staphylococcus epidermidis has been isolated predominantly from the pustules of rosacea patients but not from unaffected skin and may be transported around the face by Demodex mites. These findings raise the possibility that rosacea is fundamentally a bacterial disease resulting from the over proliferation of Demodex mites living in skin damaged as a result of adverse weathering, age or the production of sebum with an altered fatty acid content. This review surveys the literature relating to the role of Demodex mites and their associated bacteria in the induction and persistence of rosacea and highlights possible therapeutic options.
And then I did what usually causes me much anguish when I am at home - I clicked on the link for the full text, thinking that I would get a paywall.  And low and behold, I got the preprint of the paper.  The paper is quite interesting in many ways with lots of details about these mites I knew nothing about.  It also has a lot of detail on these two bacterial species and why the authors think they are of interest in rosacea etiology.  But no convincing evidence of any kind is presented that there is a causal connection to these bacteria or to these mites.  I leave everyone with the last paragraph of the paper
The pathogenic role of Demodex mites, as well as B. oleronius and S. epidermidis, in the induction and persistence of rosacea remains an unresolved issue. The lack of an immunological response to Demodex mites in healthy skin raises the possibility of localized immunosuppression, facilitating the survival of the mite. Hopefully, the results of further research will bring us closer to understanding the role of microbes in the pathogenesis of rosacea and assist in the development of new and more effective therapies for the treatment of this disfiguring disease.
I agree. Unresolved.


  1. I recall other articles that suggested overgrowth of certain bacteria in the intestines may be responsible for rosacea. The treatment is antibiotics to clear the bacteria and permit recolonization of more beneficial bacteria.
    However, the papers were also quite weak in evidence.
    I suspect we'll have a while longer until we get meaningful answers.
    For, the mites may proliferate because of additional nutrients available to them. The same is true for various bacteria.
    In all, not a lot of studies. Not a lot of evidence. Not a great deal of effective treatments.

  2. Hi Jonathan,
    This is slightly off-topic, although skin-related.

    Do you know of any correlation / causation between Malassezia and infantile / seborrheic dermatitis?


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