When it comes to phototherapy for vitiligo, one size does not fit all. Whether your disease is actively spreading or has been stable for months or years dramatically changes how light therapy should be approached — from the starting dose and frequency to the choice of combination treatments and even the primary treatment goal itself.

Understanding the difference between active and stable vitiligo is not just academic. It directly affects whether phototherapy will help you — and whether it could potentially make things worse.

Defining Active vs. Stable Vitiligo

Before discussing treatment, it is essential to understand how dermatologists determine whether vitiligo is active or stable. This classification is not based on how long you have had the condition, but on whether new patches are appearing or existing patches are expanding.

Active (Progressive) Vitiligo

A patient is considered to have active vitiligo if any of the following criteria are met, according to the Chinese Vitiligo Management Consensus:

VIDA (Vitiligo Disease Activity) score > 1: This scoring system assigns points based on when new lesions or enlargement of existing lesions last occurred — +4 for activity within 6 weeks, +3 within 3 months, +2 within 6 months, +1 within 1 year, and 0 for at least 1 year of stability. A score > 1 indicates active disease.
Koebner phenomenon: The appearance of new white patches at sites of skin trauma (cuts, friction, burns, or even phototherapy itself) within 1 year.
Wood's lamp findings: Under Wood's lamp examination, active lesions appear gray-white with indistinct borders, and the area of depigmentation seen under Wood's lamp is larger than what is visible to the naked eye.

Additional clinical features that suggest active disease include blurred patch borders, inflammatory signs (erythema, itching), trichrome vitiligo, and confetti-like lesions.

Stable Vitiligo

A patient is considered to have stable vitiligo when all of the following criteria are met:

VIDA score of 0: No new lesions or enlargement of existing lesions for at least 1 year
Clinical features: Patches are porcelain-white with sharp, well-defined borders or peripheral hyperpigmentation
No Koebner phenomenon: No trauma-induced lesions for at least 1 year
Wood's lamp findings: Lesions appear bright white with clear borders, and the area seen under Wood's lamp is equal to or smaller than the visible area

Phototherapy Protocols: Active vs. Stable

NB-UVB Phototherapy

For active vitiligo: Initiating phototherapy early is critical. Experts recommend "initiating phototherapy early in active vitiligo in order to halt disease progression". However, caution is required because the Koebner phenomenon means that even phototherapy-induced erythema could theoretically trigger new lesions in highly active disease. Starting at a lower dose and increasing more gradually is standard practice.

In a study of 150 patients treated with NB-UVB, the starting dose was 250 mJ/cm² for adults and 150 mJ/cm² for children, with 20% dose increments at each subsequent visit. Another trial protocol used an initial dose of 0.33 J/cm² with similar 20% increments. For active disease, some clinicians start even lower — around 0.2 J/cm² — and monitor closely for any signs of Koebnerization.

Treatment frequency is typically 2-3 times per week. The minimum effective course is 6-12 months, though stabilization may be observed earlier.

For stable vitiligo: Standard starting doses are typically 0.3 J/cm² for NB-UVB, with the minimal erythema dose (MED) range generally between 0.4 J/cm² and 0.8 J/cm². Higher doses can be used more aggressively since there is no risk of triggering new lesions. The focus shifts entirely to repigmentation outcomes.

In the same study of 150 patients, 73% achieved 25-75% repigmentation with an average of 51 exposures, while 26 patients (17%) achieved >75% repigmentation with an average of 74 exposures. Good response was directly associated with good compliance and higher cumulative doses (P < 0.01).

Treating vitiligo with phototherapy requires fundamentally different approaches depending on whether the disease is active or stable. In active disease, the priority is stabilization — using lower doses, combining with anti-inflammatory agents like corticosteroids, and monitoring closely for Koebnerization. In stable disease, the priority shifts to repigmentation — using standard or higher doses, combining with a broader range of topical agents, and potentially integrating surgical approaches for resistant lesions.

The 2025 Canadian Consensus Guidelines emphasize that treatment should be individualized, with phototherapy "used as monotherapy or in combination with other treatments" and disease stabilization and repigmentation as achievable goals "particularly when patients share a mutual understanding of vitiligo and its treatment options".

Before starting any phototherapy regimen, a thorough assessment of disease activity — using VIDA scoring, Wood's lamp examination, and clinical evaluation — is essential. The right approach for stable disease could be harmful in active disease, and vice versa.

Treating Stable vs. Active Vitiligo with Light Therapy: Key Differences

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