Narrowband ultraviolet B minimal erythema dose reference range.

Narrowband ultraviolet B (NB-UVB) phototherapy is a widely used treatment for various dermatological conditions. To optimize dosing and identify abnormal photosensitivity, minimal erythema dose (MED) testing is routinely performed. This retrospective review analysed MED values from 882 patients in Dundee and 188 in London, excluding those with abnormal photosensitivity or repeat tests. Median MED values increased with Fitzpatrick skin phototype (SPT), but significant overlap was observed across SPTs and between centres. Notably, Dundee exhibited statistically lower MED values than London for SPT II/III (P < 0.001). Compared with published volunteer studies, both centres reported lower MEDs, possibly due to differences in dosimetry, erythema assessment or population UV sensitivity. Nonresponder rates were low for SPT I-III but higher in SPT IV-VI, suggesting a need for broader test dose ranges in darker skin types. These findings provide updated reference ranges to inform NB-UVB phototherapy protocols and improve clinical practice.