The treatment known as PUVA , or Puvatherapy, consists in combining the supply of psoralen with exposure to ultra-violet radiation of type A (UVA), which has the role to activate the drug.

Follow-up during thirty years of a cohort of patients who had received PUVA treatment against psoriasis (administration of psoralen and UVA irradiation) to several conclusions. A) exposure to 350 or more session involves significant increased risk of squamous cell cancer, and a very moderate increase risk of basocarcinoma cell. B) The PUVA treatment with the least amount of session involves risk cancer much more reduced. Therefore, when evaluating the opportunity to implement the above-mentioned treatment in patients with psoriasis should be taken into account especially the possible risk of favoring the occurrence of squamous cell cancers.