PUVA is a combination of an oral drug and ultraviolet light therapy used to treat various skin disorders, most commonly psoriasis. The Psolaren, in PUVA, is a chemical found in certain plants that have the ability to absorb ultraviolet light in the UVA portion of the solar spectrum. Once the light energy is absorbed, the psolarens interact with DNA, inhibiting cell multiplication. Improvements are generally visible after about 15 treatments, and treatments can be given no sooner than 48 hours apart. Individual results vary, but it has proven to be very effective.