Phototherapy is often used to treat inflammatory skin conditions such as psoriasis and eczema. Much progress has recently been made in understanding the mechanisms underlying the local, cutaneous immune effects induced by phototherapy. Unlike many immunosuppressive drugs used in the management of inflammatory skin disease, phototherapy not only targets effector immune cells but also appears to up-regulate regulatory T cells (Tregs). Additionally, phototherapy reverses epidermal barrier abnormalities common in these diseases, allowing for restoration of cutaneous homeostasis.