Background: The cause of rosacea is unknown; among other factors a causative role has been postulated for the hair follicle mites Demodex folliculorum and Demodex brevis.
Objective: Our purpose was to compare the population density of Demodex mites in facial skin of defined categories of patients with rosacea with control subjects. We also assessed the impact of tetracycline therapy on the mite population.
Methods: The population density and distribution of Demodex mites were studied in the facial skin of 42 patients with rosacea and 42 age- and sex-matched control subjects. Mites were counted in measured skin surface biopsy specimens obtained from six standard facial sites with cyanoacrylate glue.
Results: The mean mite count was 49.8 (range 2 to 158) in patients with rosacea and 10.8 (range up to 97) in control subjects (p < 0.001); the highest density of mites was found on the cheeks. A statistically significant increase in mites was found in all subgroups of rosacea, being most marked in those with steroid-induced rosacea. Mite counts in patients with rosacea before and after a 1-month course of oral tetracycline showed no significant difference.
Conclusion: Increased mites may play a part in the pathogenesis of rosacea by provoking inflammatory or allergic reactions, by mechanical blockage of follicles, or by acting as vectors for microorganisms.