PUVA — Oral and Topical Psoralen Photosensitization
Psoralen molecules intercalate DNA and require UVA activation to work.
- Oral/topical: Psoralen route (8-MOP common agent)
- 1.5–2 h: Dosing window (before UVA exposure)
- 320–400 nm: UVA range (long-wave ultraviolet)
- High: Photosensitivity (eye/skin protection required)
How psoralen sensitization works
Placeholder: psoralen binds DNA and awaits UVA photoactivation.
UVA Deep Penetration Mechanism
UVA reaches deeper dermal layers than UVB, engaging sensitized cells.
- Deep dermis: Penetration depth (vs. shallow UVB)
- Mono/bi-functional: Crosslink type (psoralen-DNA adducts)
- T-lymphocytes: Target cells (and keratinocytes)
- ~20 min: Session length (typical exposure)
Depth of action
Placeholder: UVA travels past the epidermis into deeper skin layers.
NB-UVB — Narrowband UVB Without Photosensitizer
311nm UVB acts directly on epidermal cells, no pill required.
- 311 nm: Wavelength (narrowband peak)
- None: Sensitizer needed (simpler protocol)
- Epidermis: Penetration depth (shallower than UVA)
- Preferred: Pregnancy use (safer profile)
Direct epidermal action
Placeholder: NB-UVB triggers apoptosis of pathogenic T-cells directly.
Efficacy and Side-Effect Comparison
PUVA clears thicker plaques faster but carries more long-term risk.
- Faster: PUVA clearance (fewer sessions needed)
- Better: NB-UVB safety (lower carcinogenic risk)
- Skin cancer: PUVA long-term risk (cumulative dose linked)
- PUVA only: Nausea/GI effects (oral psoralen side effect)
Balancing speed against safety
Placeholder: efficacy and cumulative risk trade off between modalities.
Choosing Modality by Disease Severity
Severe thick plaques may favor PUVA; moderate disease favors NB-UVB.
- NB-UVB: Moderate disease (first-line choice)
- PUVA: Severe/thick plaques (deeper penetration helps)
- NB-UVB: Children/pregnancy (preferred safety profile)
- Limits apply: Cumulative sessions (lifetime dose tracked)
Matching therapy to patient
Placeholder: severity, skin type, and history guide the final choice.
Placeholder: shared decision-making weighs speed versus cumulative risk.