Route · Device-based

Photodynamic therapy: there is a trial against light alone

A photosensitiser is applied and then light is shone on it. In a trial against a control side given the same dose of light without the drug, acne lesion clearance was 67.4% versus 41.1%. The trials, though, enrol 20 to 30 people.

Last checked Sep 20, 2026

At a glance

Session length: 60–180 min
Pain: PainfulReported in a trialIn the trial that swapped riboflavin in for the photosensitiser, the ALA side had significantly more pain and burning during treatment (P < .001). It depends on which drug is used.
Downtime: 3–7 days
Sessions: 2–4 sessionsReported in a trialThe trials on this page used two, three and four sessions. How many is right has not been settled.
How long it lasts: Not applicable
Relative cost: Middle
How well established: Moderate evidence

“Reported in a trial” means a number a study on this page actually reported. “Typical range” is not a measured value but roughly how it is usually done, and it varies by clinic and by person.

Cost is not an amount but a band: where this procedure falls when the ones on this site are lined up per session, or per area treated. Real prices differ several-fold by clinic and by how much is treated, so they are not given here. Surgery is measured on a different scale and cannot be compared with this band.

This is not how large the effect is but how well confirmed it is. It shows the highest grade among the findings on this page.

Korean classification Being checkedThe regulatory class has not yet been confirmed against a primary document. It will be filled in once it is.

Photodynamic therapy combines two things. A photosensitiser is applied to the skin, left for a set time, and then light at the wavelength that drug responds to is shone on it.

Where the two meet, reactive oxygen is produced, and that is said to act on sebaceous glands and acne bacteria. Neither the drug alone nor the light alone produces that reaction.

In Korea it is used for acne and for actinic keratosis (pre-cancerous change in long sun-exposed skin). This page covers only the acne trials.

What makes it stand out on this site is the shape of the control group. Trials of device treatments usually compare against an untreated side; the first trial below compared against the same red light at the same dose with only the photosensitiser removed. It was designed to separate what the light does from what the drug does.

Topical options are on the adapalene, benzoyl peroxide and salicylic acid pages.

What is established

Moderate evidence

More lesions cleared than on the side given light alone

This is a 2024 trial in Shanghai. 26 people with mild-to-moderate acne had photodynamic therapy with a chlorin e6 derivative on one half of the face and, on the other half, the same dose of red light with no photosensitiser. Four sessions; 22 completed. Patients were blinded.

Lesion clearance four weeks after the final session:

Total lesions: 67.42 ± 8.51% vs 41.05 ± 11.97% (P < .001)
Inflammatory lesions: 84.41 ± 7.13% vs 50.10 ± 13.91% (P < .0001)

Sebum was also significantly lower on the treated side.

Note that the control side improved by 41%. Red light alone reduces acne. What the photosensitiser added is the 26 percentage points on top.

And there were 26 people. A single small trial cannot rule out chance. The same design needs repeating elsewhere.

Randomised controlled trial in people · 26 participants · Compared with vehicle (same formula minus the active) · Funding not declared · Endpoint clinical events (cancers, lesion counts) PMID 39226754

Moderate evidence

Swapping in riboflavin gave similar results with fewer adverse effects

The most common photosensitiser in PDT is 5-aminolevulinic acid (ALA). It works, but pain during treatment and erythema and pigmentation afterwards are problems.

A 2025 trial at Xiangya put riboflavin (vitamin B2) in its place. 33 people had each side of the face randomly assigned to riboflavin or ALA, followed by blue light. Three sessions a week apart, followed to week 10. Thirty completed.

Both sides significantly reduced inflammatory and non-inflammatory lesions at weeks 4, 6 and 10 (all P < .001).

The difference between sides was 2.6% (−4.3 to 12.5%, P = .71), which did not cross the pre-set non-inferiority margin.

The adverse effects separated them. The ALA side had more in-treatment pain and burning (P < .001), more post-treatment erythema (P = .003), more hyperpigmentation (P < .001) and more desquamation (P = .006).

'Non-inferior' is not 'better', and this is one trial of 33 people. But the two sides were on the same person, so a large difference between the drugs would likely have shown.

Randomised controlled trial in people · 33 participants · 10 weeks · Compared with another active ingredient · Funding not declared · Endpoint clinical events (cancers, lesion counts) PMID 39709022

Moderate evidence

Adding a salicylic acid peel afterwards cleared more lesions

This is a 2025 trial. In 19 people with moderate-to-severe acne, one side of the face had ALA-PDT alone and the other had ALA-PDT followed by 30% supramolecular salicylic acid. Two sessions a week apart, followed to four weeks after the last.

The sequential side reduced lesion counts significantly more, particularly comedones and papules, with no additional damage to the skin barrier reported.

There is one more thing. The sequential protocol partly attenuated the post-PDT erythema and the ultraviolet-visible pigment clusters. Mild transient pain was reported while the acid was applied.

It enrolled 19 people. That is among the smallest trials on this site, and what it establishes reaches only as far as the direction.

Randomised controlled trial in people · 19 participants · Compared with another active ingredient · Funding not declared · Endpoint clinical events (cancers, lesion counts) PMID 40420552

Known risks

Pain during treatment is the most common problem. It is worst with ALA, and the trials above were attempts to reduce it.
Erythema, swelling and peeling for several days afterwards — reported directly in the trials above.
Hyperpigmentation can follow. The darker the skin, the more this matters.
You become photosensitive. After the photosensitiser goes on, sunlight and strong indoor light must be avoided for a period that depends on the drug used. Follow the instructions from where you had it done.
Pregnancy, breastfeeding and photosensitivity disorders are things to settle in consultation first.

What is not established

We found no trial measuring how long it lasts. The trials above followed people only four to ten weeks after the last session.
How many sessions is right has no answer here. These three trials alone used two, three and four.
Which photosensitiser is best is unsettled. The riboflavin trial is one study and tested only non-inferiority.
We could not include a trial against topical or oral medication. Whether to choose this over isotretinoin or adapalene cannot be answered from this page.
Every trial enrolled 20 to 30 people, and most were run in China.

Whether to have it done is a decision to make with a doctor.

What this article relies on

PubMed — 미국 국립의학도서관 문헌 데이터베이스National Library of Medicine · Checked on 2026-09-16
Two-step photodynamic therapy for facial acne: a randomized controlled trial of pain reduction with 630 nm red light laserLasers in medical science · 2025 · PMID 40192834