The effect of phototherapy on Demodex density: a case-control study

Human Demodex mites, Demodex folliculorum and Demodex brevis, are microorganisms that reside in the pilosebaceous units, usually without causing symptoms. Phototherapy has been linked to demodicosis in previous studies. We aimed to determine whether there was an increase in the frequency of demodicosis and Demodex density after 20 phototherapy sessions.

A case-control study was conducted with 32 participants who received narrowband ultraviolet B or ultraviolet A-1 therapy for various dermatological indications. Standardized skin surface biopsies were performed before and after phototherapy to assess Demodex density. The presence of Demodex-related skin conditions was assessed before phototherapy. A statistical analysis was performed to compare the Demodex densities and prevalence of demodicosis between the baseline and 20th session of phototherapy.

No significant change was observed in Demodex density after 20 sessions of phototherapy. The average Demodex density before treatment was 2.75 ± 4.48 (/cm² ), and after treatment, it was 2.85 ± 4.81 (/cm² ), indicating no significant difference (P = 0.879). The percentage of patients with demodicosis in at least one region of the face was 28.1% (9/32) before treatment, and after treatment, it was 31.3% (10/32), with no significant difference (P = 1.00).

Our findings contradict previous studies that suggested an increased Demodex density and demodicosis prevalence after phototherapy. The data from previous studies are open to debate due to their selected samples, designs, and interpretations regarding the phototherapy-immunosuppression-Demodex relationship. Larger-scale longitudinal studies conducted on a homogeneous sample are warranted to better understand the relationship between phototherapy and demodicosis.