Answer: PUVA-photochemotherapy combining a psoralen with long-wave ultraviolet irradiation (UVA), is the latest treatment; special lamps are required.The psoralen, generally metoxsalen (unlicensed) is used to enhace the therapeutic effect of the irradiation; it may be administered either by mouth or topically.Treatment is available in hospital dermatology centres; it has to be carefully regulated, owing to the shortterm hazard of severe burning and the long term hazards of accelereated ageing of the skin, the development of skin cancer and ,unless protected cataract formation.