Phototherapy

What it is

Phototherapy (controlled therapeutic UV light exposure, predominantly narrowband UVB, with PUVA - psoralen plus UVA - as an alternative) is an established treatment for several chronic inflammatory skin diseases, exploiting UV light's local immunomodulatory effects on the skin
A well-established, effective treatment particularly for psoriasis and eczema not adequately controlled by topical therapy alone, before escalating to systemic immunosuppressive/biologic treatment

UV light induces local immunosuppression in the skin (affecting antigen-presenting cell function and T cell activity) and has direct antiproliferative effects on keratinocytes - relevant to psoriasis's pathogenic hyperproliferation - explaining efficacy across several T cell/keratinocyte-driven inflammatory dermatoses

Narrowband UVB is generally preferred over broadband UVB and PUVA given a better efficacy-to-side-effect profile and no need for the photosensitising psoralen medication PUVA requires
Treatment is given as a course of regular sessions (typically 2-3 times weekly) over weeks, with dose titrated to the individual's skin type and response, monitoring for erythema/burning as a dose-limiting toxicity

Indicated for psoriasis, atopic dermatitis, and other T cell-mediated inflammatory dermatoses not adequately controlled with topical treatment alone
Cumulative long-term UV exposure carries a skin cancer risk (more established for PUVA than narrowband UVB, though the risk is not zero for either) - relevant to counselling and long-term treatment planning, particularly for patients requiring repeated courses over years
Photosensitising medications and conditions (e.g. lupus) are relative contraindications given the risk of an exaggerated phototoxic reaction

Psoriasis, atopic dermatitis, vitiligo (a specific additional indication for narrowband UVB, promoting repigmentation), PUVA-associated skin cancer risk

The cumulative skin cancer risk associated with phototherapy, particularly PUVA, means long-term treatment planning should track cumulative exposure over a patient's lifetime, not treat each course in isolation - this is a specific, ongoing counselling point for patients requiring repeated phototherapy courses over years

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