Photodynamic Therapy – PDT
Photodynamic therapy (PDT) is a non-invasive, targeted treatment that brings together three ingredients: a light-sensitizing agent (photosensitizer) applied to the skin, a light source of matching wavelength, and the oxygen naturally present in skin tissue. It has been a major advance in treating precancerous skin lesions and early, superficial non-melanoma skin cancers (NMSC), as well as chronic pilosebaceous conditions such as nodulocystic acne, treatment-resistant cystic acne and actinic keratoses.
At Haute-Derma, we deliver PDT to international medical standards, carefully controlling the photosensitizer incubation time and the light dose and using modern pain-relief protocols. This lets us destroy diseased cells as effectively as possible while preserving the surrounding healthy skin.
How Photodynamic Therapy Works
Selective Buildup of Protoporphyrin IX (PpIX)
When a photosensitizer precursor such as 5-aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) is applied to the skin, it passes through the stratum corneum and accumulates preferentially in cells that are highly metabolically active or sit beneath a damaged skin barrier – atypical keratinocytes, tumor cells, overactive sebaceous gland cells and the bacterium Cutibacterium acnes. In these abnormal cells, the heme-making enzyme ferrochelatase is overwhelmed or underactive, so protoporphyrin IX (PpIX) piles up. PpIX is a natural photosensitizer that becomes highly toxic when exposed to light.
Type I and Type II Photo-Oxidation
When the skin is illuminated with light that matches PpIX's absorption spectrum (the Soret band peak at 415 nm and the Q-bands at 630–635 nm):
- Type I reaction: Excited PpIX reacts directly with cell membranes or other biomolecules inside the cell, generating hydroxyl and superoxide free radicals.
- Type II reaction (the main mechanism): PpIX transfers its energy directly to ground-state molecular oxygen, producing singlet oxygen (¹O₂). Singlet oxygen is a powerful oxidant that instantly damages mitochondrial and cell membranes and drives diseased cells into programmed cell death (apoptosis) or necrosis.
Effects on Sebaceous Glands and Small Blood Vessels
PDT selectively destroys sebocytes, producing long-lasting shrinkage of the sebaceous glands and a clear reduction in oiliness. At the same time, light activates the natural porphyrins made by C. acnes, killing the bacteria without fostering antibiotic resistance. In superficial skin tumors, PDT also shuts down the small vessels feeding the tumor, starving it of blood so that it regresses.
Photosensitizers and Light Sources Used in Practice
- 5-Aminolevulinic acid (ALA 20%):
- Properties: A water-soluble molecule that penetrates the stratum corneum less readily than the ester form.
- Best suited for: Moderate to severe inflammatory acne and widespread actinic keratoses on the face and scalp.
- Methyl aminolevulinate (MAL 16.8%):
- Properties: A fat-soluble ester of ALA that reaches deeper into the dermis, tumor tissue and sebaceous glands. It is also more selective for tumor cells and less painful than ALA.
- Best suited for: Actinic keratosis, superficial basal cell carcinoma (superficial BCC) and Bowen's disease (SCC in situ).
- Daylight PDT (DL-PDT):
- Properties: Natural daylight activates PpIX continuously, as soon as small amounts are formed inside the cells.
- Advantages: Almost entirely avoids the intense burning pain of high-power LED illumination, with comparable results for widespread actinic keratoses.
Comparing PDT Methods and Their Indications
| Method / Agent | Main Target Mechanism | Preferred Indications |
|---|---|---|
| ALA-PDT (blue light) | Excites PpIX at its Soret band peak, kills C. acnes and shrinks sebaceous glands | Nodulocystic acne, cystic acne, very oily skin |
| MAL-PDT (red light) | Red light penetrates 3–5 mm, generating ¹O₂ that destroys tumor tissue and dermal targets | Superficial basal cell carcinoma (sBCC), Bowen's disease, actinic keratosis |
| Daylight MAL-PDT | PpIX is formed and activated at the same time, minimizing sudden flares of pain | Widespread actinic keratoses on the face and scalp |
Clinical Safety, Pain Control and Local Side Effects
- Controlling pain during illumination: The burst of singlet oxygen strongly stimulates pain fibers in the dermis. At Haute-Derma, we actively manage this with continuous cooling mist, a dedicated cold-air device (Zimmer Cooler at −20°C) or regional nerve blocks for large treatment areas.
- Phototoxic reactions after treatment: Redness, puffy eyelids, sterile pustules and crusting are normal, expected acute inflammatory reactions. They peak at 24–48 hours and clear within 7–10 days.
- Strict light avoidance after the procedure: Leftover PpIX in the skin stays light-sensitive for about 24–48 hours after application. For the first 48 hours, patients should stay in a dim room or fully cover up with a dark fabric mask and sunglasses, and avoid bright fluorescent lighting and electronic screens.
The Treatment Process at Haute-Derma
Lesion Preparation
- The skin is cleansed, makeup is removed and the treatment area is disinfected.
- For actinic keratoses or skin tumors (BCC/Bowen's disease), surface scale is gently scraped away (curettage) or the skin is lightly microdermabraded so the photosensitizer can penetrate the target tissue better.
Application and Occluded Incubation
- An even layer of MAL 16.8% cream or ALA 20% solution is applied to the affected skin plus a 5 mm margin of normal skin.
- The area is covered with a light-blocking film and dark dressing so that ambient light cannot activate the drug too early. Incubation lasts from 1 hour (for acne) to 3 hours (for keratoses and skin tumors).
Illumination and Recovery Care
- Excess photosensitizer is rinsed off with sterile saline.
- The area is illuminated with red LED light (630 nm, 37 J/cm²) or blue LED light depending on the protocol, with Zimmer cold-air cooling for pain relief.
- Before you leave, a repair cream containing panthenol and zinc oxide is applied, followed by a tinted mineral sunscreen as a final layer of light protection.
