Phototherapy in psoriasis: a review of mechanisms of action.

Background: Phototherapy is one of the most efficacious treatment options for psoriasis. New, emerging studies are beginning to define the biologic mechanisms by which phototherapy improves psoriasis.

Methods: To provide an overview of the mechanisms thought to be responsible for the therapeutic effects of phototherapy, a review was performed on all relevant published studies in the Medline database from January 1, 1985, to August 15, 2011.

Findings: Four categories of action were proposed in the literature to describe the effects of phototherapy in psoriasis: (1) alteration of the cytokine profile, (2) induction of apoptosis, (3) promotion of immunosuppression, and (4) all other mechanisms.

Conclusions: Phototherapy acts through a combination of pathways to confer therapeutic benefits in psoriasis, and these different modalities may help explain its particular usefulness in treating this cutaneous disease.