Bath-PUVA therapy improves impaired resting regulatory T cells and increases circulating activated regulatory T cells in psoriasis

•Psoriasis may be due to a regulatory T cell (Treg) imbalance.•Bath-psoralen plus ultraviolet light A (PUVA) therapy is effective for psoriasis.•Activated Treg, which suppress psoriatic activity, are increased by Bath-PUVA.•Resting Treg, which are low in psoriasis patients, are increased by Bath-PUVA.•Bath-PUVA may improve the Treg imbalance in psoriasis.