Mechanism, indications, practice economics, and equipment know-how — collected from five decades around medical lasers. Educational content only; treatment decisions belong to you and your device labeling.
308 nm UVB efficiently induces apoptosis of pathogenic T lymphocytes in psoriatic plaques — more potently per unit dose than broadband or narrowband UVB — interrupting the inflammatory cascade that drives keratinocyte hyperproliferation.
In vitiligo, 308 nm exposure stimulates migration and proliferation of melanocytes from the follicular reservoir and promotes local immunomodulation — the basis for repigmentation, especially on the face and neck.
Because the beam treats only lesional skin, doses of 2–6× MED can be delivered where whole-body cabinets can't go beyond ~1× MED. Result: fewer sessions to clearance and longer remissions reported versus conventional NB-UVB.
Click through the major indications. Typical course lengths reflect commonly published ranges — individual protocols depend on skin type, MED, and site.
The excimer laser is FDA-cleared for psoriasis and shines for localized, recalcitrant plaques: elbows, knees, scalp, palms, and soles — the sites that resist topicals and frustrate patients.
Targeted 308 nm therapy is a mainstay for localized vitiligo, with facial and neck lesions responding best. Combination with topical calcineurin inhibitors or corticosteroids is common practice and frequently additive.
For chronic localized atopic dermatitis — especially lichenified plaques and prurigo-like lesions — targeted UVB offers steroid-sparing control without systemic exposure.
Published series report regrowth in patchy alopecia areata treated with 308 nm excimer laser, particularly in children and on the scalp, likely via local immunomodulation of the peribulbar T-cell attack.
The literature describes targeted 308 nm use in a range of additional dermatoses — generally where localized immunomodulation helps and systemic therapy is undesirable:
Off-label applications — evaluate the evidence and your device labeling before extending indications.
Laser phototherapy has a clean, well-established CPT pathway based on treated surface area.
| CPT Code | Description | Practice notes |
|---|---|---|
| 96920 | Laser treatment of inflammatory skin disease (psoriasis); total area < 250 sq cm | The bread-and-butter code for localized plaque treatment |
| 96921 | Laser treatment; 250–500 sq cm | Multiple plaques or larger fields in one session |
| 96922 | Laser treatment; over 500 sq cm | Extensive disease; verify payer policies on frequency |
A well-run laser earns more and fails less. Five habits worth institutionalizing:
| Term | Meaning |
|---|---|
| Excimer | "Excited dimer" — here, xenon chloride (XeCl) molecules that exist only in an excited state and emit 308 nm light when they dissociate. |
| MED | Minimal Erythema Dose — the smallest UV dose producing perceptible redness at 24 h; the anchor for dosing protocols. |
| mJ/cm² | Millijoules per square centimeter — the unit of delivered UV dose (fluence). |
| Fluence | Energy delivered per unit area; what you're actually prescribing each session. |
| Supra-erythemogenic dosing | Deliberately dosing above 1× MED on lesional skin — the targeted-therapy advantage. |
| Koebnerization | New psoriasis lesions arising at sites of skin injury — why aggressive blistering doses warrant caution. |
| NB-UVB | Narrowband UVB (~311 nm) from fluorescent cabinets — the whole-body cousin of excimer therapy. |
| Thyratron | The high-voltage switch that fires the discharge — a classic excimer wear component. |