Although they are normal inhabitants of human skin and cannot be seen, microscopic mites known as Demodex folliculorum may actually be something to blush about, as a new study funded by the National Rosacea Society demonstrated for the first time that these invisible organisms may be a cause or exacerbating factor in rosacea.¹

"While it is well established that Demodex occur in far greater numbers on the faces of people with rosacea, it was uncertain whether they play a role in the development of the disorder," said Dr. Frank Powell, consultant dermatologist at Mater Misericordiae Hospital in Dublin, Ireland, who conducted the study along with colleagues at the National University of Ireland-Maynooth. "In other words, which came first, the mites or the rosacea? And now there is evidence that it might be the mites."

In the new study, published in the British Journal of Dermatology, the researchers identified Bacillus oleronius as distinct bacteria associated with Demodex mites. When analyzing blood samples using a peripheral blood mononuclear cell proliferation assay, they found that B. oleronius stimulated an immune system response in 79 percent of 22 patients with subtype 2 (papulopustular) rosacea, compared with only 29 percent of 17 subjects without the disorder.

"The immune response results in inflammation, as evident in the papules (bumps) and pustules (pimples) of subtype 2 rosacea," Dr. Powell said. "This suggests that these bacteria found in the mites could be responsible for the inflammation associated with rosacea."

Dr. Powell noted that the potential role for the bacteria in subtype 2 (papulopustular) rosacea is also supported by the fact that effective treatment includes antibiotics that destroy B. oleronius. Interestingly, he said, antibiotics that are not harmful to these bacteria generally are not effective in the management of rosacea.

"Although the mechanism of antibiotics in treating rosacea is not definitively understood, it has long been suggested that they work through anti-inflammatory action," he said. "However, other anti-inflammatory drugs are ineffective in treating rosacea, and immunosuppressive agents, such as steroids can ultimately make the inflammation worse."

The researchers concluded that their study shows consideration must also be given to the potential for the appropriate antibiotic to affect microorganisms such as B. oleronius or other follicular or mite-related bacteria.

Associated Reference

1. Lacey N, Delaney S, Kavanagh K, Powell FC. Mite-related bacterial antigens stimulate inflammatory cells in rosacea. British Journal of Dermatology. 2007; 157:474-481.