The significance of Demodex folliculorum density in rosacea

Background Demodex folliculorum has been reported in rosacea in a number of clinical studies. As the Demodex mite is also present in many healthy individuals, it has been suggested that the mite may have a pathogenic role only when it is present in high densities. Moreover, some authors have proposed that a mite density above 5/cm(2) may be a criterion for the diagnosis of inflammatory rosacea. In this study, the possible role of D. folliculorum and the importance of mite density in rosacea were investigated using a skin surface biopsy technique. Methods Thirty-eight patients with rosacea and 38 age-and-sex-matched healthy subjects entered the study. With the skin surface biopsy technique, we obtained samples from three facial sites. We then determined the mite positivities, the mean mite counts in both study groups, the mean mite densities at each facial site and in the rosacea subgroups, and the mite densities above 5/cm2. Results The mean mite count in the rosacea group (6.684) was significantly higher than that in controls (2.868; p < 0.05). The cheek was the most frequently and heavily infested facial region. Ten rosacea patients and five normal subjects had mite densities over 5/ cm(2); the difference was not statistically significant (p > 0.05). Conclusions Rosacea is a disease of multifactorial origin, and individual properties may modify the severity of the inflammatory response to Demodex. We suggest that a certain mite density is not an appropriate criterion in the diagnosis of the disease; nevertheless, large numbers of D. folliculorum may have an important role in the pathogenesis of rosacea, together with other triggering factors.