In short. Narrowband UVB and targeted excimer light: how they work, how many sessions a fair trial takes, and the cumulative dose limits that matter.
Key points
- Sessions accumulate, and the dose stays with the skin for life.
- A plan that states a target number of sessions, reviews progress at intervals, and stops when the response plateaus is better medicine than an open-ended standing order.
Phototherapy is the mainstay of treatment when vitiligo involves more than a small area. It uses ultraviolet light to calm the immune attack in the skin and to stimulate the surviving melanocytes in hair follicles to divide and migrate into the depigmented patch. The two forms in common use are narrowband UVB cabinets, which treat the whole body, and targeted devices such as excimer light, which treat individual patches.
Narrowband UVB
Narrowband UVB uses a narrow slice of the ultraviolet spectrum, chosen because it is effective in vitiligo and avoids the burning wavelengths of older broadband treatment. The person stands in a cabinet for a short time, two or three times a week. Treatment starts at a low dose and increases gradually, guided by how the skin responds. It is the standard choice for widespread or bilateral disease.
Targeted excimer light delivers the same wavelengths to a defined area, which allows a higher dose to the patch while sparing the rest of the skin. It is useful for limited or localised disease, for the face, and for people who cannot manage full-body sessions.
How many sessions
Phototherapy is slow work. A fair trial is counted in months rather than weeks, and typically involves dozens of sessions, commonly somewhere between thirty and a hundred depending on the site and the response. Repigmentation usually begins as small dark spots around hair follicles, which gradually enlarge and merge. The face and neck respond best, the trunk responds reasonably, and the hands, feet and lips respond poorly, where pigment may never return.
There is a point at which continuing is not useful. If there has been no response at all after a substantial course, the realistic option is to stop and reconsider rather than continue indefinitely.
Cumulative dose and safety
Ultraviolet is not harmless, and the total dose accumulates over a lifetime. Prolonged phototherapy increases the risk of sunburn, premature skin ageing and skin cancer, and this risk is greater in people who have received many courses over many years or who also take photosensitising medicines. For that reason treatment is dosed carefully, the total number of sessions is tracked rather than left open-ended, and the skin is examined periodically. Protective eyewear and shielding of unaffected skin are standard.
Burns are the commonest immediate problem, and they matter more in vitiligo than in most conditions, because injured skin can develop new patches. Doses are increased cautiously for that reason.
Phototherapy is a course, not a habit
Sessions accumulate, and the dose stays with the skin for life. A plan that states a target number of sessions, reviews progress at intervals, and stops when the response plateaus is better medicine than an open-ended standing order.
Stop and seek advice if
- The skin becomes red, blistered or painful after a session.
- New patches of pigment loss appear during treatment.
- You are taking a medicine that makes the skin more sensitive to light.
Frequently asked questions
How many sessions does a fair trial of phototherapy take?
A fair trial is counted in months rather than weeks and typically involves dozens of sessions, commonly somewhere between thirty and a hundred depending on the site and the response. If there has been no response at all after a substantial course, the realistic option is to stop and reconsider.
What is the difference between a narrowband UVB cabinet and targeted excimer light?
A narrowband UVB cabinet treats the whole body and is the standard choice for widespread or bilateral disease. Targeted excimer light delivers the same wavelengths to a defined area, which allows a higher dose to the patch while sparing the rest of the skin. It suits limited or localised disease and the face.
What are the long-term concerns about the total amount of ultraviolet received?
The total dose accumulates over a lifetime. Prolonged phototherapy increases the risk of sunburn, premature skin ageing and skin cancer, and the risk is greater after many courses over many years or in people who also take photosensitising medicines. Sessions are therefore tracked rather than left open-ended.
Risks & Limitations
- Repigmentation is slow, measured in months to years, and is often partial rather than complete.
- Vitiligo is unpredictable: treatment can control it, but nothing guarantees that it will stop spreading.
- Treatment usually needs to continue to hold the result, and relapse is common after it is stopped.
- Prolonged topical steroid use can thin the skin, cause visible blood vessels and stretch marks, and trigger outbreaks of small spots around the hair follicles.
- Phototherapy can burn, and the ultraviolet dose accumulates over a lifetime, raising the risk of skin ageing and skin cancer.
- The face and neck respond best; the hands, feet and lips are the hardest areas, where pigment may never return.
- No treatment works for everyone, and the response of an individual patch cannot be predicted with certainty.
When to Seek Care
- Depigmentation is spreading rapidly, or new patches are appearing over weeks rather than months.
- Depigmentation involves the eyelids or the skin around the eyes.
- New symptoms suggest a thyroid or other autoimmune condition — persistent fatigue, weight change, feeling cold, a neck swelling, or excessive thirst.
- Blistering, burning or severe pain after a phototherapy session — stop treatment and seek advice.
- Eye pain, redness, light sensitivity or blurred vision, which need prompt assessment.
References & Further Reading
- American Academy of Dermatology (AAD) — public and clinical guidance on vitiligo
- Vitiligo Research Foundation — patient and clinician information resources
- Cochrane Library — systematic reviews of vitiligo treatment
- Chinese Medical Association, Dermatology Branch — clinical guidance
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.