Narrowband UVB Phototherapy in Dark Skin: Initiation and Adjustment
For patients with dark skin (Fitzpatrick skin phototypes IV-VI), start narrowband UVB at 400 mJ/cm² (or 50% of MED if testing is performed) and increase by 15-65 mJ/cm² per session, treating 3 times weekly—but recognize that these patients require broader test dose ranges, higher cumulative doses, and more treatment sessions to achieve clearance compared to lighter skin types.
Starting Dose Selection
The standard approach uses either:
- Skin phototype-based dosing: 400 mJ/cm² for darker skin types (IV-VI) 1
- MED-based dosing: 50% of the minimal erythema dose 2, 1
However, recent evidence reveals a critical limitation: nonresponder rates are significantly higher in Fitzpatrick skin types IV-VI, suggesting that standard test dose ranges are inadequate for darker skin 3. This means the conventional starting doses may be too conservative for many dark-skinned patients.
Key Pitfall to Avoid
MED testing in darker skin is less reliable due to difficulty visualizing erythema. Only 30% of dermatologists perform MED testing in practice 4, and when they do, visual assessment methods are standard—which are inherently less accurate in pigmented skin 3. If you cannot reliably perform or read MED testing in dark skin, use the higher end of skin phototype-based dosing (400 mJ/cm²) rather than underestimating the starting dose.
Dose Escalation Protocol
Increase by 15-65 mJ/cm² per treatment (or 10% of the initial MED if MED-based) 1. The guideline recommends the more conservative 20% increments reducing to 10% approach rather than 40% reducing to 20%, as the latter causes increased painful erythema 2.
For dark skin specifically:
- Expect to need higher cumulative doses than published for lighter skin types 5
- Plan for more treatment sessions to achieve clearance—in one study of darker-skinned patients, complete remission required a mean of 42.9 treatments and 58.11 J/cm² cumulative dose 5
- Treatment frequency: 3 times weekly is standard 1
Monitoring and Adjustment
What to Watch For:
- Erythema development: Approximately 60% of patients develop erythema by session 20 regardless of skin type 6, but this is harder to detect in dark skin
- Hyperpigmentation: Occurs in 4% of darker-skinned patients and is a specific concern 5
- Treatment response timing: Expect initial improvement after 8-10 treatments, with clearance typically requiring 15-20 treatments in lighter skin 1—but significantly more in dark skin 5
Critical Clinical Point:
Photoadaptation occurs equally across all skin types when measured per physical unit of UVR 6. This means the 70/20% regimen (starting at 70% MED with 20% increments) works equally well for all Fitzpatrick types I-IV in terms of erythema risk 6. However, this evidence doesn't extend to types V-VI, where the challenge is achieving adequate dosing rather than avoiding burns.
Practical Algorithm for Dark Skin
- Start at 400 mJ/cm² (upper range for skin type-based dosing) unless MED testing reliably shows a different value
- Increase by 20% per session for the first 10 treatments
- Reduce increments to 10% after session 10 to minimize erythema risk
- Assess response at 20 treatments: If inadequate response, consider that dark skin may need 40+ treatments 5
- Continue to higher cumulative doses than you would for lighter skin—don't prematurely discontinue assuming treatment failure
Special Considerations
Maintenance therapy: After achieving clearance, maintenance treatment is recommended, though optimal schedules vary 1. In darker-skinned patients with mycosis fungoides, 40% relapsed within 5 months after discontinuing maintenance 5.
Combination therapy: When combining with acitretin, reduce both UVB and retinoid doses by approximately 25% 1. Start acitretin 2 weeks before phototherapy initiation.
The fundamental challenge in dark skin is that standard protocols were developed primarily for lighter skin types, leading to systematic underdosing in darker patients 3, 5. Adjust your expectations for treatment duration and cumulative dose requirements accordingly.