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Dr. Chen Yi-Jia · Dermatology Notes
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Latest Research · Photodynamic Therapy

Photodynamic Therapy (PDT): A Complete Dermatology Guide
From AK and BCC to acne — synthesis of two 2026 JAAD CME Reviews

In June 2026, the Journal of the American Academy of Dermatology published two CME Reviews on photodynamic therapy (PDT): Part I covers mechanism and photosensitizers (Austin et al.), Part II covers 12 dermatologic clinical applications (Wang et al.). This article integrates both into a patient + clinician dual-track guide. PDT = photosensitizer + light + oxygen → reactive oxygen species that selectively damage lesional cells while sparing surrounding tissue. The strongest evidence (LoE IA) is for actinic keratoses, basal cell carcinoma, Bowen disease, and acne; eight additional indications include port wine stain, photoaging, rosacea, alopecia areata, and mycosis fungoides.

~20 min read Last reviewed 2026-05-23 ‍️ Dr. Chen Yi-Jia
Reminder · This article summarizes two 2026 JAAD CME Reviews for general medical education only; it does not constitute individual medical advice. PDT regimens, photosensitizer/light source selection, and session counts require individualized assessment by a dermatologist based on lesion type, location, depth, skin phototype, and patient tolerance.
One-page TL;DR — three numbers to know
  • 1. AK clearance rate: 5-ALA + blue light achieves 77-89% clearance on face/scalp at 3 months, comparable to or better than cryotherapy / imiquimod / 5-FU, with superior cosmetic outcomes. FDA-approved since 1999.
  • 2. Superficial / low-risk BCC: MAL or BF-200 ALA + red light, two sessions, clearance 92-97% at 3 months; 9% recurrence at 1 year, 22% at 5 years. Slightly higher recurrence than surgery but superior cosmetic outcomes.
  • 3. Moderate-to-severe acne: ALA + red light shows efficacy comparable to isotretinoin (0.5 mg/kg/day × 6 mo) with more rapid onset. 6-month recurrence: 24% PDT vs 38% isotretinoin (non-significant).

Why does dermatology use light? A brief 100-year history

Phototherapy in dermatology spans millennia — ancient Egypt, India, and China used sunlight for psoriasis, vitiligo, and skin cancer. In 1903 Niels Finsen won the Nobel Prize for treating cutaneous tuberculosis with carbon arc light. In the early 1900s, Oscar Raab and Hermann von Tappeiner first described "photodynamic action" — the therapeutic interaction of photosensitizer + light + oxygen. After 5-ALA became available in the 1990s and the FDA approved the first PDT indication (actinic keratosis) in 1999, PDT expanded from lesion-directed treatment to field cancerization, and into acne and photoaging. The 2022 global PDT market was ~$4.5B, projected to reach $8.6B by 2030.

For patients: 7 most-asked questions

Q1. What is photodynamic therapy (PDT)? How is it different from laser?

PDT combines a photosensitizer, light, and oxygen. The procedure: apply a photosensitizing cream (most commonly 5-ALA or MAL) to the lesion, wait 1-3 hours for abnormal cells to absorb it, then illuminate with specific-wavelength light (red or blue). The drug, activated by light, generates reactive oxygen species (ROS) that destroy abnormal cells.

Differences from laser:

  • Laser uses photothermal action directly without pre-applied drug; PDT uses photochemical action and requires drug pre-incubation.
  • Laser damage is target-molecule-dependent (melanin, hemoglobin); PDT selectivity is higher because abnormal cells accumulate more photosensitizer due to altered enzyme activity, sparing normal tissue.
  • ⏱ Laser: usually completes in one short visit. PDT: 2-4 hours per session due to incubation time.
  • 🩹 Laser may leave punctate burn marks; PDT rarely scars and suits face/scalp where cosmesis matters.

Q2. Which skin conditions can PDT treat? Which can it not?

The 2026 JAAD review identified 12 evidence-based indications, sorted by Level of Evidence (LoE):

Strongest evidence (LoE IA, multiple RCTs and meta-analyses):

  • Actinic keratosis (AK, sun-damaged keratotic lesions) — the only FDA-approved indication
  • Superficial basal cell carcinoma and low-risk nodular BCC
  • Bowen disease (cutaneous SCC in situ)
  • Moderate-to-severe acne vulgaris — effective for both inflammatory and non-inflammatory lesions

Moderate evidence (LoE IB-II):

  • Port wine stain (PWS) — intravenous Hemoporfin + KTP laser (approved in China)
  • Photoaging — improves fine lines, texture, and tone
  • Actinic cheilitis — the lip equivalent of AK
  • HPV warts, herpes simplex, cutaneous MRSA infections

Early evidence (LoE III-IV, mostly case series):

  • Mycosis fungoides (most common form of cutaneous T-cell lymphoma)
  • Rosacea — reduces erythema and inflammatory papules
  • Alopecia areata (AA) — early evidence, not first-line
  • Extramammary Paget disease (EMPD) — palliative, does not replace surgery

NOT suitable for PDT:

  • Infiltrative or high-risk BCC (eyelids, nose, ears, lips, ≥2 cm, recurrent) — needs Mohs surgery
  • Invasive SCC — requires surgery or radiation
  • Melanoma — absolute contraindication; PDT ineffective for deep lesions
  • Pregnancy, porphyria, photosensitizer hypersensitivity

Q3. Does it hurt? Is anesthesia needed?

Yes — and pain is PDT's most-cited downside. About 16-20% of patients experience severe pain, peaking within the first 7-10 minutes of irradiation and gradually subsiding. The cause is ROS-induced stimulation of cutaneous nerves and release of inflammatory mediators.

Pain modifiers:

  • Larger treatment areas are more painful (face/scalp > single lesion)
  • Lesion type: AK > BCC > Bowen disease in pain severity
  • Light source: red light typically less painful than blue light
  • ALA may be slightly more painful than MAL, though evidence is inconsistent

Pain management options (efficacy from RCT):

  • Nerve block (scalp nerve block superior to cold air + IV analgesia)
  • Cold-air analgesia — convective cold air, simple/cheap, moderate effect
  • Topical anesthetics (lidocaine, prilocaine) applied 30 min pre-treatment
  • Talk therapy — engaging conversation during treatment reduces anxiety and pain perception (RCT-validated)
  • Switch to daylight PDT — apply drug then expose to natural sunlight for 2h; significantly less painful with non-inferior efficacy

IV sedation and general anesthesia are not standard. Key point: severe pain causing premature discontinuation lowers efficacy — discuss your pain tolerance and management plan with your dermatologist beforehand.

Q4. What happens to the skin after treatment? How long until recovery?

PDT triggers a predictable inflammatory response:

  • ⏱ 0-2h: phototoxic reaction peaks — redness, swelling, burning, stinging
  • Days 1-3: erythema and edema visible, possible exudate, crusts begin forming
  • Days 4-7: crusting phase — looks like "skin allergy" or sunburn peeling, itchy
  • Weeks 1-2: crusts shed, skin recovers, mild residual redness
  • Weeks 2-4: erythema fades, skin returns to near-baseline appearance with lesion cleared

Post-treatment care:

  • MOST IMPORTANT: avoid direct sunlight and bright light for 40 hours post-treatment — residual photosensitizer can still be light-activated, causing serious burns. Wear hat + physical sunscreen + long sleeves outdoors
  • During crusting: don't pick or peel — gentle warm-water cleansing + thin layer of white petrolatum
  • No makeup for 1 week (may seed into crusts, infection risk); use fragrance-free, alcohol-free sunscreen
  • Return immediately if: yellow-green pus, fever, persistent redness/swelling beyond 2 weeks, blisters, or purpura

Q5. How does it compare with surgery / cryotherapy / 5-FU / imiquimod?

Comparison for the two best-evidenced indications (AK and BCC):

TreatmentClearanceCosmesisPainField Tx
PDTAK 77-89%, BCC 92-97%SuperiorModerate-high Treats whole field at once
Surgical excisionBCC ~97% at 1yScarWith anesthesia Single lesion
CryotherapyAK ~70%, comparable or slightly lessMay depigmentModerate Per-lesion
Imiquimod 5%AK ~50-60%, self-apply 4-16 wkGoodMild-mod (red, itch) Requires adherence
5-FU 5%AK ~50-70%, 2-4 wk topicalGoodHigh (red, erosion)

Bottom line:

  • Multiple lesions or field disease → PDT or topical agents beat single-site surgery
  • Face/scalp/visible areas where cosmesis matters → PDT scars least
  • Single deep / ill-defined / recurrent / ≥2 cm lesion → surgery is the answer
  • Prefer home-based, can adhere to topical regimens → topical imiquimod / 5-FU
  • Few lesions, not concerned with transient pigment change → cryotherapy is cheap and fast

Q6. How many sessions are needed? When will results show?

Session count varies by indication:

  • AK: 1-2 sessions, 4-12 weeks apart, clearance assessed at 3 months
  • BCC / Bowen disease: 2 sessions 1 week apart (European standard), 3-month assessment, follow-up within 1 year
  • Moderate-to-severe acne: 2-5 sessions, 1-2 weeks apart, visible improvement at 6-12 weeks; may need repeat courses
  • Photoaging / rosacea: 2-3 sessions monthly, results gradual over 2-3 months
  • PWS: Hemoporfin protocol, 2 sessions 2 months apart (Chinese protocol)

The acne PDT vs isotretinoin comparison is striking: an RCT found ALA + RL × 2 sessions matched isotretinoin 0.5 mg/kg/day × 6 months in reducing inflammation and sebum, with faster onset and lower 6-month recurrence (24% vs 38%, non-significant). PDT is a reasonable alternative for patients who can't take isotretinoin (planning pregnancy, liver concerns, contraception adherence issues).

Q7. Am I a good candidate? Which conditions are contraindicated?

Good PDT candidates:

  • Multiple AKs scattered on face, scalp, dorsal hands (field treatment)
  • Superficial BCC, single <2 cm, outside the H-zone
  • Moderate-to-severe acne, isotretinoin contraindicated or refused
  • Lesions in cosmetically sensitive areas — PDT rarely scars
  • Patients unable to comply with surgery or long topical regimens (elderly, limited mobility)

Caution required:

  • Darker skin types (Fitzpatrick V-VI) — risk of pigmentary change, requires lesion-depth + light-source review
  • On photosensitizing meds (doxycycline, amiodarone, certain diuretics, sulfonamides) — consider hold pre-treatment
  • Active autoimmune disease (e.g. lupus) — PDT may trigger flare

Absolute contraindications:

  • Porphyria (cutaneous porphyria) — PDT mechanism (PpIX accumulation) triggers acute flare
  • Hypersensitivity to photosensitizers (ALA, MAL) or other ingredients
  • Pregnancy (insufficient safety data)
  • Infiltrative / high-risk BCC, invasive SCC, melanoma
  • Active infection at treatment site (cellulitis, active HSV)

Pre-visit checklist: (1) list all current meds and supplements; (2) report allergies and prior photosensitivity reactions; (3) discuss pregnancy plans; (4) ask: which photosensitizer (ALA vs MAL), which light source (RL vs BL vs daylight), how many sessions, treatment-day duration, post-care.

Further reading: For actinic keratosis (AK) and cutaneous squamous cell carcinoma (SCC) full guide see AK and SCC: complete patient guide; for other moderate-to-severe acne options see Isotretinoin patient guide; for the overall rosacea treatment strategy see 6 rosacea myths.

Below: clinical write-up · for clinicians

The three pillars of PDT and molecular mechanism

Modern PDT requires three elements: (1) a photosensitizer (PS) that selectively accumulates in lesional cells; (2) a light source matched to the PS absorption peak; (3) molecular oxygen (³O₂) in tissue. All three are essential.

The PS absorbs a photon and transitions from ground to excited singlet, then via intersystem crossing to the triplet state. The triplet PS reacts with molecular oxygen via two pathways:

  • Type II (dominant): energy transfer to ³O₂ → singlet oxygen (¹O₂). ¹O₂ half-life only 40 ns, range 20 nm — high spatial selectivity, sparing surrounding tissue.
  • Type I (minor): PS reacts directly with substrate → superoxide, hydroxyl radicals, H₂O₂ (ROS). Austin et al. showed ALA-PDT + BL in human dermal fibroblasts produces predominantly superoxide; no measurable hydroxyl ROS or H₂O₂.

¹O₂ and ROS trigger downstream: (a) intrinsic apoptosis (caspase 3/7/8, BAX/BAK upregulation, BCL-2 downregulation); (b) extrinsic Fas/CD95 pathway; (c) vascular endothelial damage and microvessel thrombosis cutting off tumor supply; (d) DAMP and cytokine release activating immune response and antitumor memory.

Figure 1: PDT molecular mechanism PDT triad → ROS → three downstream effects Photosensitizer PS / PpIX Light source RL/BL/daylight Molecular oxygen ³O₂ ROS ¹O₂ half-life 40 ns Apoptosis apoptosis / mitochondria Vascular damage Endothelial apoptosis / microthrombi Immune activation DAMPs / cytokines
Figure 1 — The three PDT inputs (PS + light + oxygen) react in tissue to produce ROS (mostly ¹O₂; half-life 40 ns, 20 nm radius), triggering three major downstream effects: apoptosis, vascular damage, immune activation. Adapted from Austin EJ et al. JAAD 2026;94:1619-32 Fig 1.

Photosensitizers: ALA vs MAL — why neoplastic cells accumulate more PpIX

The two most common topical PS are prodrugs — non-photosensitizing themselves, they are metabolized via the heme biosynthesis pathway into protoporphyrin IX (PpIX), the actual photosensitizing molecule. PpIX has a primary absorption peak at 410 nm (violet, in the blue spectrum) and smaller peaks at 505, 540, 580, 640 nm (green/yellow/orange/red).

The selectivity principle: cancer and some dysplastic cells have decreased ferrochelatase activity (the enzyme converting PpIX → heme). Reduced activity → PpIX builds up. Meanwhile, exogenous ALA bypasses the rate-limiting ALA synthase step in heme biosynthesis, further driving PpIX accumulation. Net result: cancerous/abnormal cells reach far higher intracellular PpIX than surrounding normal tissue, enabling selective phototoxicity.

Figure 2: ALA / MAL → PpIX metabolism ALA / MAL → PpIX metabolism and selectivity principle Normal cell Normal cell ALA → PBG → intermediates → PpIX ─→ heme Normal ferrochelatase activity PpIX rapidly metabolized → heme PpIX accumulation ≈ low Mild damage under light Cancer / abnormal cell Cancer cell ALA → PBG → intermediates → PpIX ─╳ heme Ferrochelatase activity ↓ PpIX accumulates — metabolic bottleneck PpIX accumulation ≈ high Selective phototoxicity under light
Figure 2 — ALA and MAL are prodrugs for PpIX. Cancer cells have decreased ferrochelatase activity, blocking PpIX→heme conversion. The resulting metabolic bottleneck drives intracellular PpIX accumulation far above normal cells — the basis of PDT selectivity.

ALA vs MAL comparison

Item5-ALAMAL
PropertiesHydrophilic, MW 167 DaLipophilic, methylated ALA, MW 145 Da
PenetrationModerate stratum corneum penetration, longer incubation (1-3 h)Deeper lipophilic penetration, shorter incubation possible
Tumor selectivityHigh, slightly lower than MALHigher; MAL must be converted intracellularly to ALA via enzymatic steps, increasing tumor specificity
PainSlightly higher (inconsistent evidence)Slightly lower
US FDA 20% solution Levulan Kerastick (DUSA), 10% nanoscale-lipid gel Ameluz (Biofrontera) Not approved
EU / Canada Ameluz 16.8% Metvix (Galderma)
Other PS in dermmethylene blue, indocyanine green, porfimer sodium, hemoporfin (China-approved for PWS), temoporfin

Light source selection: red, blue, daylight, laser

Light penetration depth correlates with wavelength and inversely with photon energy. Short wavelengths (e.g. blue) carry more energy per photon but penetrate less; long wavelengths (e.g. red) penetrate deeper but per-photon energy is lower. Clinical choice depends on lesion depth and superficial-vs-deep distribution:

Figure 3: Penetration depth by light source PDT light source — penetration depth comparison (skin layers) Stratum corneum ~ 0.1 mm Epidermis ~ 0.5 mm Dermis ~ 2-4 mm Subcutis Blue light (BL) 400-500 nm Green light (GL) 500-565 nm Red light (RL) 625-700 nm Near-infrared 700-1100 nm BL: superficial AK / surface acne GL: intermediate depth RL: BCC, deep AK, acne IR: deep lesions or ICG combo
Figure 3 — Light penetration by wavelength: blue light (BL, 400-500 nm) penetrates 0.5-2 mm to epidermis — best for superficial AK / acne; red light (RL, 625-700 nm) reaches 0.5-10 mm into dermis — best for BCC and deeper lesions; green light is intermediate; near-infrared (IR) requires matched PS such as ICG.

Light source types

SourceWavelengthProsCons
LEDBL 410、RL 630-660Low heat, moderate cost, uniform fluenceFixed area, limited precision
FluorescentBL（BLU-U 405-420）Cheap, widely usedImpure spectrum, variable output
Pulsed dye laser585-595High precision, deep, dual vascular targetingExpensive, burn risk
Intense pulsed light500-1200（broadband）Broadband, versatileBroadband less efficient at PpIX activation
Daylight PDTFull spectrum (400-700)No clinic device, pain significantly lower, high satisfaction, non-inferior efficacy (meta-analysis)Weather-dependent, superficial only

LoE ladder for 12 indications with standard protocols

The 2026 JAAD Wang et al. review identifies 12 dermatologic PDT applications, ranked by Level of Evidence. LoE IA = multiple consistent RCTs + meta-analyses; LoE II-IV = case series or single trials.

Figure 4: 12 indications by evidence ladder LoE ladder for the 12 PDT indications LoE IA — strongest evidence (multiple RCTs + meta-analyses) 1. Actinic keratosis (AK) — sole FDA-approved indication, 77-89% 2. Superficial/low-risk BCC (92-97%) | 3. Bowen disease (77-82%) | 4. Moderate-severe acne LoE IB-II — moderate evidence (single RCT or multiple cohorts) 5. Port-wine stain (Hemoporfin + KTP, China-approved) 6. Photoaging | 7. Actinic cheilitis 8. Skin infections (HPV warts, MRSA, HSV, leishmaniasis) LoE III-IV — early evidence (case series, small trials) 9. Mycosis fungoides (CTCL) 10. Rosacea | 11. Alopecia areata 12. Extramammary Paget disease (palliative, not a surgery substitute) Not suitable for PDT Infiltrative / high-risk BCC, invasive SCC, melanoma, porphyria, pregnancy
Figure 4 — Twelve dermatologic PDT applications ranked by Level of Evidence. LoE IA (green): strongest evidence from multiple RCTs and meta-analyses; LoE IB-II (yellow): moderate evidence; LoE III-IV (red): early evidence; bottom gray bar: contraindications. Synthesized from Wang JY et al. JAAD 2026;94:1635-50.

LoE IA: actinic keratoses

In 1999, FDA approved the first PDT indication for non-hyperkeratotic facial / scalp AK. Standard protocol: 20% ALA solution (Levulan Kerastick) + BLU-U blue light (10 J/cm²), 1 h incubation. Clearance at 3 months: face/scalp 77-89%, upper extremities 70-81%. Meta-analysis conclusions:

  • ALA-PDT + RL outperforms cryotherapy, imiquimod, 5-FU (3 meta-analyses)
  • BF-200 ALA (Ameluz) outperforms MAL (3 meta-analyses)
  • Daylight MAL-PDT non-inferior to conventional PDT, fewer AEs, higher satisfaction (3 meta-analyses)
  • Field-directed superior to lesion-directed; prevents field cancerization

Lesion prep tips: curette thick crusts; 30% urea cream BID × 7 d as keratolytic; microneedling or low-energy laser pre-treatment can substantially enhance PS penetration. 10% BF-200 ALA requires occlusion at all sites; 20% ALA only requires occlusion on upper extremities.

LoE IA: basal cell carcinoma

The 2023 European Dermatology Forum consensus: PDT effectively treats superficial BCC and low-risk nodular BCC. Low-risk = <2 cm, well-defined borders, no prior treatment, outside the H-zone (periorbital, nasal alae, lips, ears).

Standard protocol: 16% MAL or BF-200 ALA, 3 h incubation, RL 37-75 J/cm², weekly × 2 sessions. Phase III RCT data:

  • Complete response at 3 mo: 92-97% (MAL ≈ ALA)
  • 1-year recurrence: 9%
  • 5-year recurrence: 22%
  • Vs surgery: lower clearance (PDT 93% vs surgery 99%), higher recurrence, but superior cosmesis
  • Vs cryotherapy / 5-FU: comparable response rates (4 meta-analyses)

Do NOT use for:

  • Infiltrative, morpheaform, micronodular BCC
  • ≥2 cm or H-zone lesions (eyelids, nose, ears, lips)
  • Recurrent BCC
  • Gorlin syndrome deep lesions (superficial still considerable)

Lesion curettage (debulking) before PDT improves clearance for thicker BCC.

LoE IA: Bowen disease (SCC in situ)

77-82%
Meta-analysis clearance (12-24 mo)
81% vs 71%
ALA-PDT outperforms MAL-PDT
82% vs 97%
PDT vs surgery 1-yr clearance

Outperforms cryotherapy and 5-FU; lower clearance than surgery but particularly suitable for large or multiple lesions, distal extremities, low-perfusion sites, or high-surgical-risk patients.

LoE IA: moderate-to-severe acne

Acne PDT mechanism: (a) PpIX accumulates in sebaceous glands → selective gland destruction, reducing sebum; (b) anti-inflammatory effect (apoptosis of inflammatory infiltrate); (c) direct antimicrobial action on C. acnes.

Useful PS: 5-ALA, MAL, indole-3-acetic acid (IAA) + green light, indocyanine green (ICG) + NIR, methylene blue. Most effective combinations (per Wang review): ALA + sunlight, ICG + NIR LED, IAA + green LED.

Key RCT: ALA-PDT + RL × 2 sessions vs adapalene 0.1% gel + doxycycline 100 mg/d × 6 wk — PDT significantly outperformed for both inflammatory and non-inflammatory lesion reduction. Another RCT in moderate-to-severe acne: ALA + RL × 2 sessions vs isotretinoin 0.5 mg/kg/d × 6 mo — comparable efficacy at 2/4/6 mo, PDT faster onset, 6-mo recurrence PDT 24% vs isotretinoin 38% (NS).

LoE IB-II: PWS, photoaging, others

  • PWS: China-approved protocol — Hemoporfin 5 mg/kg IV + KTP laser (532 nm) 96-120 J/cm² × 2 sessions 2 mo apart. Effective for PDL-resistant violet PWS.
  • Photoaging: 5-20% ALA incubation 30 min-3 h + RL 50-100 J/cm² or BL 10 J/cm² × 2-3 sessions monthly. Improves fine lines, texture, dyspigmentation.
  • Actinic cheilitis: lip equivalent of AK — MAL or ALA + RL, 3-mo clearance 50-80%.
  • Skin infections: HPV warts, HSV (especially recurrent), cutaneous MRSA, leishmaniasis — case series and small trials. Methylene blue suits MRSA; ICG suits HSV.

LoE III-IV: early / exploratory indications

  • Mycosis fungoides: early patch / plaque stage — MAL + RL, case series CR 50-75%, option for those unfit for surgery/radiation.
  • Rosacea: ALA-PDT + RL improves erythematotelangiectatic and papulopustular rosacea (small RCTs).
  • Alopecia areata: early case series, hypothesized immune modulation mechanism, not first-line.
  • EMPD: palliative for unresectable or margin-positive cases, does not replace surgery.

Pain management ladder

Pain is PDT's most-cited downside — 16-20% experience severe pain, sometimes causing premature discontinuation → reduced efficacy. Time course: pain begins 0-3 min into illumination, peaks at 5-10 min, declines after 7-10 min. Histamine peaks ~30 min post-illumination.

Figure 5: Pain-management ladder PDT pain-management ladder (by RCT evidence) First-line (strongest evidence) Scalp nerve block (RCT-proven superior to cold-air + IV analgesia) Second-line (simple, cheap, moderate) Cold-air analgesia (blower-style cooler) Adjunct: topical anesthesia + psychological support Topical lidocaine/prilocaine 30 min pre-treatment; talk therapy (distraction) is RCT-supported Change protocol Switch to daylight PDT (significantly less painful, superficial only); switch to RL (slightly less painful than BL) Note: IV sedation / general anesthesia are non-standard, reserved for special cases (children, very large fields).
Figure 5 — PDT pain management ladder. Scalp nerve block is the most RCT-validated single intervention; cold-air analgesia is the most-used first-line in most clinics; topical anesthetics and talk therapy are adjuncts; switching to daylight PDT is the most fundamental pain reduction but limited to superficial lesions (AK).

Emerging trends: thermal PDT and daylight PDT

New protocol · shorter visits

Thermal PDT — heat-assisted photodynamic therapy

Heat the skin to 33-42°C during incubation (still clinically tolerable) to accelerate the PS → PpIX enzymatic conversion.

Skin temperature
33-42°C
Incubation time
15-30 min (vs. 1-3 h conventional)
Light source
Same as conventional (RL / BL)
Pros: Shorter clinic visits, higher patient satisfaction, non-inferior or superior efficacy in recent RCTs.
New protocol · least painful

Daylight PDT — natural-sunlight photodynamic

Apply MAL / ALA, wait 30 minutes, then expose to natural sunlight outdoors for 2 hours. Low intensity + long duration → PpIX is continuously consumed, dramatically reducing pain.

Photosensitizer
MAL or ALA
Indoor wait
30 min absorption
Sunlight exposure
2 hours (90-120 min optimal)
Weather requirements
Clear / partly cloudy, ≥ 10°C
Pros: Pain dramatically reduced, high patient satisfaction, non-inferior efficacy to conventional PDT (3 meta-analyses).
Limitations: Superficial lesions only (AK, superficial BCC, acne); not feasible in poor weather; avoid in rain or below 10°C.

Adverse events, contraindications, post-care

Short-term AEs:

  • Pain, burning (peaks during and 0-2 h post)
  • Erythema, edema (24-72 h)
  • Exudate (1-3 d)
  • Crusting and desquamation (4-14 d)
  • Pruritus, transient hypo/hyperpigmentation
  • Rare (<1%): vesicular reaction, secondary infection, scarring

Long-term safety: current evidence shows no cumulative toxicity or carcinogenic effect; multi-year repeat treatment has no significant adverse impact on skin function.

40-hour post-treatment photoprotection: residual photosensitizer persists ~24-48 h. During this period:

  • Strictly avoid direct sunlight and bright indoor light (surgical lamps, strong LED bulbs, car window light)
  • Outdoors: wide-brim hat, sunglasses, long sleeves, physical sunscreen (SPF 50+)
  • Chemical sunscreen alone is insufficient against visible light — physical ZnO/TiO₂ required

Clinical practice take-aways

  1. Three pillars: photosensitizer + light + oxygen. Most common PS = 5-ALA and MAL; both prodrugs metabolized to PpIX intracellularly.
  2. Cancer cells have ↓ ferrochelatase activity → PpIX accumulation → selective phototoxicity.
  3. Light source: superficial lesions (AK, surface acne) → BL (efficient); deeper lesions (BCC, Bowen, deeper acne) → RL (penetrating).
  4. LoE IA indications: AK, superficial / low-risk BCC, Bowen disease, moderate-to-severe acne. AK is the only FDA-approved indication (since 1999).
  5. Acne PDT especially valuable for isotretinoin-ineligible patients — comparable efficacy, faster onset, lower recurrence (24% vs 38%, NS).
  6. Daylight PDT for superficial AK: significantly less painful, non-inferior efficacy, higher satisfaction — a trend direction.
  7. Absolute contraindications: porphyria, PS hypersensitivity, pregnancy, infiltrative / high-risk BCC / SCC / melanoma.
  8. 40-h post-treatment photoprotection is mandatory — physical sunscreen + hat + long sleeves; chemical sunscreen alone is insufficient against visible light.

References

  1. Austin EJ, Wang JY, Ozog DM, Zeitouni N, Lim HW, Jagdeo J. Photodynamic therapy: Overview and mechanism of action. J Am Acad Dermatol. 2026;94(6):1619-1632. doi:10.1016/j.jaad.2025.02.037
  2. Wang JY, Zeitouni N, Austin EJ, Jagdeo J, Lim HW, Ozog DM. Photodynamic therapy: Clinical applications in dermatology. J Am Acad Dermatol. 2026;94(6):1635-1650. doi:10.1016/j.jaad.2024.12.050
  3. European Dermatology Forum. Updated S3 European consensus guidelines for the treatment of actinic keratosis and basal cell carcinoma using photodynamic therapy. J Eur Acad Dermatol Venereol. 2023.
  4. Morton CA, Szeimies RM, Basset-Seguin N, et al. European Dermatology Forum guidelines on topical photodynamic therapy 2019 Part 1: treatment delivery and established indications. J Eur Acad Dermatol Venereol. 2019;33(12):2225-2238.
  5. Yan P, Liu LH, Yu MY, et al. Topical photodynamic therapy with 5-aminolevulinic acid for basal cell carcinoma: a meta-analysis. Photodiagnosis Photodyn Ther. 2021;36:102511.
  6. Liang H, Cao Y, Gao Y, et al. Comparison of photodynamic therapy and cryotherapy for actinic keratosis: a meta-analysis. Br J Dermatol. 2022;186(4):587-595.
  7. Lang K, Schulte KW, Ruzicka T, Fritsch C. Aminolevulinic acid (Levulan) in photodynamic therapy of actinic keratoses. Skin Therapy Lett. 2001;6(10):1-2,5.
  8. Foley P, Freeman M, Menter A, et al. Photodynamic therapy with methyl aminolevulinate for primary nodular basal cell carcinoma: results of two randomized studies. Int J Dermatol. 2009;48(11):1236-1245.
  9. An JS, Jin SY, Han GH, et al. A randomized controlled trial of 5-aminolevulinic acid photodynamic therapy and oral isotretinoin for moderate-to-severe acne. J Dermatol. 2022;49(4):432-438.
  10. Zhao Y, Tu P, Zhou G, et al. Hemoporfin photodynamic therapy for port wine stain: a randomized controlled trial. PLoS One. 2016;11(11):e0165308.
  11. Lacour JP, Ulrich C, Gilaberte Y, et al. Daylight photodynamic therapy with methyl aminolevulinate cream is effective and nearly painless in treating actinic keratoses: a randomised, investigator-blinded, controlled, phase III study. J Eur Acad Dermatol Venereol. 2015;29(12):2342-2348.
  12. Halldin CB, Paoli J, Sandberg C, Gonzalez H, Wennberg AM. Nerve blocks enable adequate pain relief during topical photodynamic therapy of field cancerization on the forehead and scalp. Br J Dermatol. 2009;160(4):795-800.