How Photodynamic Therapy (PDT) for Acne Works

Photodynamic therapy (PDT) is a noninvasive therapy that uses light treatments along with an application of a photosensitizing agent, typically 5-aminolevulinic acid (ALA). The photosensitizing agent is applied to the skin, causing the skin to become more susceptible, or receptive, to light.

After the photosensitizing agent is applied, light treatment is administered. PDT was originally approved by the Food and Drug Administration (FDA) to treat cancer and is often used to treat actinic keratosis, rough, scaly patches on the skin caused by long-term sun exposure. It is now being studied as a safe and effective treatment for acne.

Photodynamic Therapy
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How It Works

PDT is thought to work by shrinking the skin's oil glands. This can reduce the amount of oil within the pores, thereby reducing comedones. For those with moderate-to-severe acne that doesn't respond well to traditional topical treatments, this is good news.

ALA-PDT may also kill bacteria that cause acne breakouts and normalize the shedding of dead skin cells within the follicle. It also seems to improve the skin's overall texture and holds promise in the repair of acne scarring.

Many patients participating in early photodynamic therapy trials reported moderate-to-severe pain. However, treatments administered today apply gel to the skin for a shorter period of time. Most patients now report a mildly uncomfortable feeling, like experiencing a slight sunburn.

Most short-contact photodynamic therapy treatments start with microdermabrasion, to remove excess dead cells on the skin's surface and enhance ALA penetration. Next, the photosensitizing agent (ALA) is applied to the skin. The skin is then treated—usually with blue light—immediately for a period of 30–60 minutes.

In another method, after the ALA has been allowed to set for an hour, the skin is treated with blue light for about 16 minutes. Both regimens have been found equally effective, but immediate light therapy is reported to be significantly less painful.

A series of three to five treatments is usually performed in two- to four-week intervals. The number of treatments recommended depends on the severity of acne. Some patients may notice results after the first treatment. Photodynamic therapy can be used in conjunction with other acne treatments, such as topical retinoids or salicylic acid.


The results of ALA-PDT for acne treatments arepromising. Some studies have shown a significant improvement of acne breakouts, improvement of skin texture, and the softening and reduction of acne scars. A few patients have even reported a 50%–75% improvement in their acne. PDT can be used to treat moderate-to-severe cystic acne and may provide results similar to those achieved with Accutane (isotretinoin, a drug to treat severe acne).

Possible Side Effects

The side effects of short-contact photodynamic therapy may include redness and/or peeling of the treatment site that's similar to a sunburn. The burn is generally mild and resolves quickly.

Unfortunately, photodynamic therapy treatments can cost more than conventional acne treatments, and they are not often covered by insurance. However, systemic medications usually prescribed for severe acne, such as Accutane, have serious side effects that short-contact ALA-PDT does not. Photodynamic therapy may provide an effective alternative to systemic medications.

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  1. Kaw U, et al. A regimen to minimize pain during blue light photodynamic therapy of actinic keratoses: Bilaterally controlled, randomized trial of simultaneous versus conventional illumination. Journal of the American Academy of Dermatology. 2020;82(4):862-868. doi:10.1016/j.jaad.2019.09.010