🎨 Narrowband UVB Phototherapy Simulator

311nm Narrowband UVB — Precision Wavelength Phototherapy

Narrow 311nm band targets melanocyte pathways with minimal burn risk.

• 311 nm: Wavelength (narrowband UVB peak)
• 2-3x/wk: Typical frequency (per treatment protocol)
• mJ/cm²: Starting dose (titrated by skin type)
• Seconds: Session length (short controlled exposure)

Why 311nm is used

Narrowband targets pigment pathways while sparing surrounding tissue.

Hair Follicle Bulge — The Melanocyte Stem Cell Reservoir

UVB wakes dormant melanocyte stem cells housed in the follicle bulge.

• Bulge: Reservoir site (outer root sheath region)
• McSC: Cell type (melanocyte stem cells)
• UVB: Trigger (photobiologic activation signal)
• Hair density: Dependence (more follicles, more reservoirs)

Reservoir activation

Follicle density strongly predicts how much reservoir is available.

Melanocyte Precursor Migration Toward Depigmented Skin

Activated precursors migrate along the follicle shaft into the epidermis.

• Follicle→epidermis: Path (outward radial migration)
• Chemokines: Driver (signal gradients guide cells)
• Weeks: Speed (gradual outward spread)
• Radial: Pattern (symmetric around follicle)

Migration mechanism

Cells crawl outward guided by local signaling gradients.

Perifollicular Pigmentation — Early Visible Repigmentation

Small pigmented dots form rings around each hair follicle opening.

• Dots: Appearance (perifollicular pigment islands)
• ~8-12 wks: Onset (after regular treatment)
• Follicular: Pattern type (classic repigmentation pattern)
• Clinical exam: Visibility (photographed for tracking)

Dot pattern significance

Dot density around follicles signals treatment is working.

Confluent Repigmentation — Merging Pigment Over Months

Pigment dots enlarge and merge into continuous repigmented skin.

• Months: Timeframe (typically 6-15 months)
• Confluence: Outcome (dots merge into patches)
• Face/neck: Best sites (high follicle density areas)
• Follicle count: Limiting factor (acral skin responds slower)

Long-term outcome

Confluence rate depends on follicle density and adherence.

More sessions and higher follicle density both speed confluent repigmentation.