Background and Aim: Psoriasis is a chronic inflammatory dermatosis that affects 0.6% to 4.8% of the general population. Our aim was to compare the effect of narrow band UVB (NB-UVB) on normal flora of cutaneous plaques and normal skin in psoriatic patients.

Methods: Twenty psoriatic patients without any contraindication of phototherapy were enrolled in this study. Samples from psoriatic lesions and adjacent normal skin, before and after phototherapy with NB-UVB were taken. Patients were treated with NB-UVB three times weekly until complete remission. Finally, quantity of normal cutaneous flora on normal and involved skin, before and after treatment was compared.

Results: The mean±SD of the NB-UVB sessions and the mean cumulative dose were 26.35±4.95 and 2.05±0.57 J/cm², respectively. The number of Staphylococcus epidermidis, S. aureus and diphtheroids on psoriatic plaques reduced after phototherapy.

Conclusuion: The quantity of normal cutaneous flora on normal skin is less than psoriatic plaques, and it reduced on normal and involved skin after phototherapy.