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Phototherapy
Phototherapy uses defined wavelengths of ultraviolet light to suppress skin inflammation — mainly by destroying activated T cells and shifting cytokines — and is an effective and inexpensive treatment for psoriasis, atopic dermatitis, vitiligo and early mycosis fungoides.
Why it matters in the exam
The exam asks which type of phototherapy suits which disease, the wavelengths, and the side effects and contraindications. NB-UVB (311 nm) is the treatment of choice in most cases and is safe in pregnancy (with folic acid supplement); PUVA (psoralen with UVA) is very effective for thick plaques and mycosis fungoides but raises the SCC risk after many treatments and requires eye protection because of cataract; UVA1 suits morphea; and the excimer laser (308 nm) targets limited lesions. Contraindications are photosensitive diseases such as lupus, xeroderma pigmentosum and porphyrias, and a history of melanoma. Remember that treatment is given two to three times a week for many weeks, that the dose is set by skin type or by minimal erythema dose testing, and that the cumulative dose must be recorded. Adherence is the main limitation because of the need for many clinic visits. Many questions also show a patient taking a photosensitising drug, such as a thiazide, tetracycline or amiodarone, and ask whether to adjust the dose. In the exam, link each disease to the right type of light and remember that home phototherapy is a good alternative for patients who struggle to attend.
Key points
- Phototherapy suppresses skin inflammation with defined UV wavelengths.
- NB-UVB (311 nm) is the treatment of choice in most cases and is safe in pregnancy.
- PUVA is effective for thick plaques and MF, but raises the SCC risk and requires eye protection.
- UVA1 suits morphea, and the excimer laser (308 nm) suits limited lesions.
- Contraindications include lupus, xeroderma pigmentosum, porphyrias and a history of melanoma.
Summary table
| Type | Wavelength | Main indications | Risks and notes |
|---|---|---|---|
| NB-UVB | 311 nm | Psoriasis, atopic dermatitis, vitiligo, early MF, chronic itch | Burning, herpes reactivation; safe in pregnancy; low cancer risk |
| PUVA | Psoralen with UVA (320–400 nm) | Thick psoriasis, palmoplantar psoriasis, MF | SCC after many treatments, cataract, nausea; protective glasses on treatment day |
| UVA1 | 340–400 nm | Morphea, acute atopic dermatitis | Penetrates deep into the dermis |
| Excimer laser | 308 nm | Limited lesions: scalp psoriasis, vitiligo | Spares healthy skin from exposure |
| Contraindications | — | Lupus, xeroderma pigmentosum, porphyrias, history of melanoma | Photosensitising drugs — reconsider |
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Sources
- Joint AAD-NPF guidelines of care for the management of psoriasis with phototherapy, 2019 — NB-UVB, PUVA and excimer
- British Photodermatology Group guidelines for narrowband UVB, 2022 — Indications and safety
- British Association of Dermatologists guidelines for topical and oral PUVA, 2016 — Safety
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.