What are the indications, dosing schedule, contraindications, side effects, and alternative treatments for narrow-band ultraviolet B (NB‑UVB) phototherapy in dermatology?

Narrowband UVB Phototherapy in Dermatology

Primary Indications

Narrowband UVB (NB-UVB) is the first-line phototherapy for psoriasis and atopic dermatitis when topical treatments fail, and is also first-line for vitiligo, polymorphic light eruption, and early-stage mycosis fungoides. 1

Strong Evidence (Grade A) Indications:

• Psoriasis (plaque and guttate): NB-UVB is more effective than broadband UVB and approaches PUVA in efficacy for skin types I-III, requiring an average of 15-20 treatments for clearance 1
• Atopic dermatitis: Superior to broadband UVA and visible light placebo, with 90% effectiveness when combined with emollients 1
• Polymorphic light eruption: Equivalent efficacy to PUVA for desensitization 1

Moderate Evidence (Grade B) Indications:

• Vitiligo: 53-92% of patients achieve >75% repigmentation, with facial and small areas responding better than acral sites 1
• Mycosis fungoides (early stage): Effective and well-tolerated, though UVB signature mutations in p53 gene raise concerns about potential disease progression 1
• Seborrheic dermatitis, pruritus, erythropoietic protoporphyria, actinic prurigo 1

Limited Evidence (Grade C) Indications:

• Lichen planus, subcorneal pustular dermatosis, nodular prurigo, granuloma annulare, alopecia areata 1, 2

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Dosing Schedule

Initial Dosing (Based on Skin Type):

Start with skin type-based dosing rather than percentage increments to minimize erythema risk 1:

Skin Type	Initial Dose (mJ/cm²)	Increment (mJ/cm²)	Maximum Dose (mJ/cm²)
I	130	15	2000
II	220	25	2000
III	260	40	3000
IV	330	45	3000
V	350	60	5000
VI	400	65	5000

Alternative MED-based approach: Start at 50% of minimal erythema dose (MED), increase by 10% of initial MED for treatments 1-20 1

Treatment Frequency:

• Administer 3-5 times per week for optimal results; attending >2.5 sessions weekly yields 62% clearance vs. 17% with <2 sessions weekly 1, 3
• Twice-weekly regimens are acceptable but require longer treatment courses 1

Dose Adjustments for Missed Treatments:

• 4-7 days missed: Keep dose the same 1
• 1-2 weeks missed: Decrease dose by 25% 1
• 2-3 weeks missed: Decrease dose by 50% or restart 1
• 3-4 weeks missed: Start over 1

Maintenance Therapy (After ≥95% Clearance):

• Once weekly for 4 weeks: Keep dose the same 1
• Once every 2 weeks for 4 weeks: Decrease dose by 25% 1
• Once every 4 weeks: Use 50% of highest dose 1
• Many patients require once-weekly NB-UVB indefinitely for long-term maintenance 1

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Absolute Contraindications

Do not use NB-UVB in patients with:

• Lupus erythematosus 1
• Xeroderma pigmentosum 1
• Porphyria (all forms) – phototherapy causes severe phototoxic injury from psoralen photo-activation 4

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Relative Contraindications & Cautions

Exercise caution in:

• Skin types I-II who burn easily 1
• History of melanoma or multiple nonmelanoma skin cancers 1
• Previous arsenic intake (Fowler solution) or ionizing radiation therapy 1
• Heat intolerance, heart disease, or claustrophobia (heat generated in light box) 1
• Pityriasis rubra pilaris (adult form may worsen; use with extreme caution) 1

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Side Effects

Short-Term:

• Erythema (most common) – minimize by using fixed increments rather than percentage-based increases 1, 5
• Pruritus and burning sensation 1
• Feeling faint in light box from heat generation 1
• Herpes simplex reactivation (2/77 pediatric patients) 1

Long-Term:

• Photoaging: Accelerated wrinkling, lentigines, telangiectasias 1
• Tanning (expected effect) 1
• Skin cancer risk: A large study of 3,867 patients (median 29 treatments, 352 patients >100 treatments) found no significant association with basal cell carcinoma, squamous cell carcinoma, or melanoma at median 5.5-year follow-up 1. However, yearly skin cancer surveillance is mandatory 1

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Safety Protocols

Genital Shielding:

• Men: Use athletic supporter or sock; rotate waistband position to treat all non-genital skin 1
• Women: Shield nipples with SPF 50 sunscreen or zinc oxide paste covering entire areola 1

Facial Protection:

• Shield face with towel or bag if no facial lesions present 1
• If facial psoriasis exists: Minimize dose to face as facial lesions respond to lower doses than trunk/extremities 1

Sunscreen Use:

• Do NOT apply sunscreen before NB-UVB on treatment day – creates uneven tolerance and potential burning 1
• Apply SPF 30 sunscreen on non-treatment days and after phototherapy, reapplying every 2-3 hours outdoors 1
• Avoid all sun tanning and tanning beds during and after NB-UVB treatment 1

Topical Agents:

• Do NOT apply oils before treatment unless specifically directed for selected areas 1
• Apply topical agents POST-UVB exposure to avoid UVB-blocking effects 1

Eye Protection:

• Use protective goggles during all treatments 1

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Special Populations

Pregnancy:

Pregnancy is NOT a contraindication to NB-UVB – it should be considered first-line therapy for pregnant patients with plaque/guttate psoriasis requiring systemic treatment, as it has no known teratogenic effects 1

Pediatric Use:

• Effective and well-tolerated in children: 63% clearance rate in psoriasis, 53% achieved >75% repigmentation in vitiligo 1
• Anxiety was significant concern in 5/77 children; make phototherapy unit child-friendly 1
• Use as second-line therapy when topicals fail 1

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Combination Therapy

Effective Combinations:

• Tazarotene + NB-UVB: Greater PASI reduction than NB-UVB alone 1
• Calcipotriol + NB-UVB: Conflicting data; may reduce cumulative UVB exposure 1

Avoid:

• Systemic retinoids + NB-UVB: No real advantage; increased relapse rate despite reduced cumulative UVB dose (Grade D recommendation) 1
• Psoralen + NB-UVB: Carcinogenicity concerns from multiple DNA photoproducts 1

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Alternative Treatments

When NB-UVB Fails or Is Contraindicated:

• PUVA (psoralen + UVA): More effective than NB-UVB for high baseline PASI scores and large plaque disease, but higher side-effect burden 1
• UVA1 phototherapy: More effective for acute atopic dermatitis flares 1
• Excimer laser (308-nm): Targets individual lesions, deeper penetration 1
• Systemic therapies: Biologics, methotrexate, cyclosporine for refractory disease 2

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Monitoring Requirements

Baseline:

• Full-body skin examination before initiating therapy 1
• Screen for personal/family history of lupus, xeroderma pigmentosum, porphyria, photosensitivity, or unexplained blistering 4

Ongoing:

• Report any erythema or discomfort to phototherapy nurse before each treatment 1
• Regular full-skin examinations to monitor photoaging, pigmentation, and cutaneous malignancies 1
• Yearly skin cancer surveillance for all patients treated with UV light 1
• Meter UVB machine weekly – lamps steadily lose power; failure to calibrate leads to false dosing impressions 1

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Common Pitfalls

• Using percentage increments instead of fixed increments increases erythema risk 1, 3
• Applying sunscreen or oils before treatment creates uneven skin tolerance and burning 1
• Inadequate genital/nipple shielding risks phototoxic reactions 1
• Failing to adjust dose for missed treatments causes burns 1
• Not calibrating UV output weekly leads to under- or over-dosing 1