Psoriasis is a common chronic inflammatory skin condition that causes substantial disability in affected people and their families. In the linked randomised controlled trial (doi:10.1136/bmj.b1542), Koek and colleagues assess whether home ultraviolet B (UVB) phototherapy is as safe and effective for psoriasis as conventional UVB phototherapy given in the outpatient department.1

UVB has been used to treat psoriasis for more than 75 years, initially in combination with crude coal tar,2 and later as monotherapy.3 UVB has been the phototherapy of choice for psoriasis since it was found to be less carcinogenic than PUVA (psoralen plus ultraviolet A phototherapy),4 and since the development in the late 1980s of a highly efficacious UVB lamp, termed “narrow band UVB.”5

Patients taking a course of UVB treatment usually attend their local dermatology unit three times each week for eight to 10 weeks. In many cases …