How Aminolevulinic Acid Photodynamic Therapy Works?

Aminolevulinic acid photodynamic therapy works by turning a chemical that skin cells naturally make into a light-activated drug. You apply aminolevulinic acid to the skin. The treated cells convert it into a photosensitive compound called protoporphyrin IX. When a specific wavelength of light hits that compound, it reacts with oxygen and damages the cells that built it up. The body then clears the damaged tissue.

That is the whole idea in one paragraph. The details matter, though, because this therapy is used for several different skin conditions, and the way it is applied changes depending on what is being treated.

What Is Aminolevulinic Acid Photodynamic Therapy?

It is a two-step treatment. A topical solution or patch delivers aminolevulinic acid to the skin. After a waiting period, a light source activates the drug that has built up inside the cells.

Aminolevulinic acid sits early in the heme synthesis pathway. Every cell uses this pathway to make heme, the iron-containing molecule in hemoglobin. In normal cells, the pathway runs efficiently and aminolevulinic acid gets converted quickly through several steps to heme. When you flood the skin with extra aminolevulinic acid, the pathway gets overloaded. Intermediate compounds pile up. One of those intermediates is protoporphyrin IX, a molecule that absorbs light strongly.

That buildup is the key. Protoporphyrin IX is a photosensitizer. It absorbs light and transfers that energy to nearby oxygen molecules, creating reactive oxygen species. These are short-lived and destructive. They damage proteins, lipids, and cell membranes in the immediate area. Cells that accumulated the most protoporphyrin IX take the most damage.

The FDA approved aminolevulinic acid with blue light for treating actinic keratosis, a common precancerous skin lesion. It has also been studied and used for certain superficial skin cancers and other conditions. Some of these uses are well established. Others are still being researched.

Why Do Treated Cells Build Up More Protoporphyrin IX Than Normal Cells?

This is the part that makes the therapy selective. Not all cells handle aminolevulinic acid the same way.

Actinic keratoses and certain skin cancer cells tend to take up more aminolevulinic acid and convert it less efficiently to heme. The result is a higher concentration of protoporphyrin IX inside those abnormal cells compared with surrounding healthy skin. The exact reasons are not fully understood, but research points to differences in enzyme activity and cell turnover rates.

Healthy skin cells also produce some protoporphyrin IX after treatment. That is why side effects like redness and peeling happen in the treated area. The selectivity is relative, not absolute. Damaged or rapidly dividing cells accumulate more of the photosensitizer, so they absorb more of the light-triggered damage.

This selectivity is one reason photodynamic therapy is appealing for superficial skin conditions. It targets abnormal tissue while largely sparing deeper structures. It is not a perfect system, and it is not appropriate for every lesion or every patient.

What Happens During a Treatment Session?

The steps are straightforward, but the timing and light source vary by condition and by the specific product used.

• The clinician prepares the skin, sometimes gently removing scales from the lesion so the medication penetrates.
• Aminolevulinic acid is applied to the treatment area. Depending on the product, it may be a solution, gel, or patch.
• The area is covered with a light-blocking dressing or left open, depending on the protocol.
• An incubation period follows. This allows the skin to convert aminolevulinic acid into protoporphyrin IX. Incubation times range from about one hour to several hours depending on the product and the condition being treated.
• The covering is removed, and the area is exposed to a specific light source. Blue light is common for actinic keratosis. Red light penetrates deeper and is used for some other applications.
• The light exposure itself typically takes minutes to under half an hour.

Most people describe the light step as a burning or stinging sensation. The intensity varies. Cooling with fans or cold air during treatment is common. Afterward, the treated area is usually red and may swell. Peeling and crusting follow over the next several days to a couple of weeks.

Some clinicians use daylight instead of an artificial light source for certain cases of actinic keratosis. Daylight photodynamic therapy uses natural sunlight to activate the drug. Research has compared daylight and conventional light sources, and results suggest daylight can be effective for some patients with less pain. Protocols differ, and not every clinic offers it.

What Conditions Is It Used For?

The best-established use is actinic keratosis. These rough, scaly patches develop on sun-exposed skin and can, in some cases, progress to squamous cell carcinoma. Treating them reduces that risk.

Photodynamic therapy with aminolevulinic acid has also been used for:

• Superficial basal cell carcinoma, a common type of skin cancer that rarely spreads but can grow locally
• Squamous cell carcinoma in situ, also called Bowen’s disease
• Acne, though evidence for this use is more limited and it is not a first-line treatment
• Certain other skin conditions, often in research settings

For invasive or deeper skin cancers, photodynamic therapy is generally not the right choice because light does not penetrate deeply enough to treat the full tumor. Surgery or other treatments are typically preferred for those cases.

How Does It Compare to Other Treatments?

For actinic keratosis, several treatments exist. Cryotherapy freezes the lesions. Topical medications like fluorouracil or imiquimod are applied at home over weeks. Photodynamic therapy is another option.

Each approach has trade-offs. Cryotherapy is quick but can cause blistering and sometimes leaves light or dark spots. Topical treatments work well but require weeks of daily application and can cause significant skin reactions. Photodynamic therapy is done in a clinic, treats a field of skin rather than individual spots, and typically requires one to a few sessions.

Which is best depends on the number and location of lesions, the patient’s preferences, and the clinician’s judgment. Research has compared these treatments, and no single option is clearly superior for every situation. Photodynamic therapy tends to be favored when there are many lesions across a broad area, such as the scalp or forehead.

What Are the Risks and Limitations?

Photodynamic therapy is generally well tolerated, but it is not without side effects.

Common reactions include pain during light exposure, redness, swelling, peeling, and crusting in the treated area. These usually resolve over one to two weeks. Temporary changes in skin color can occur. Some people develop a sensitivity to sunlight for a day or two after treatment, which is why sun protection is important during recovery.

Rare but serious reactions have been reported, including allergic reactions to the medication. Scarring is uncommon but possible.

Effectiveness varies. Some lesions clear completely after one treatment. Others need repeat sessions. Some do not respond at all. Actinic keratosis can also recur, since the underlying sun damage remains. Photodynamic therapy treats existing lesions but does not undo years of ultraviolet exposure.

Another limitation is depth. Light only penetrates so far into the skin. Lesions that are thick or deep may not be fully treated. That is why proper diagnosis and lesion selection matter. A clinician needs to confirm what is being treated before choosing this approach.

Is This Therapy Right for Everyone?

No. Photodynamic therapy is not appropriate for all skin conditions or all patients.

It is generally not used for invasive skin cancers or lesions that extend too deep for light to reach. People with certain photosensitive conditions, such as porphyria, may not be candidates. Pregnancy and breastfeeding status should be discussed with a clinician, as safety data in these groups is limited.

Anyone considering this treatment should have a proper diagnosis first. Not every rough patch on sun-exposed skin is an actinic keratosis. Some are benign. Some are skin cancers that need a different approach. A biopsy or clinical evaluation by a dermatologist is often part of the process.

If you are considering photodynamic therapy, ask your clinician about the specific product and light source they plan to use, how many sessions you might need, and what to expect during recovery. The answers will depend on your individual situation.