What Is Photodynamic Therapy?

Photodynamic therapy (PDT) is a treatment that uses light and a special type of medicine, called a photosensitizer, to kill cancerous and precancerous skin growths. When the light hits the photosensitizer, it activates it, which causes a chemical reaction.

PDT is most commonly used to treat skin conditions like actinic keratosis (precancerous skin lesions) and superficial skin cancers, as well as certain types of acne. But recent studies have shown that it is effective in treating other types of cancers and health conditions.

Here’s what to know about how PDT works, what conditions it can treat, and what to expect before, during, and after the procedure.

There are two types of photodynamic therapy.

• Conventional (Clinic-Based) Photodynamic Therapy This type of PDT uses either laser or LED lights to activate the photosynthesizer.
• Daylight Photodynamic Therapy (dPDT) In dPDT, the photosensitizer is activated by natural sunlight rather than an indoor light source. To avoid sun damage to the skin, a chemical sunscreen is applied before the treatment.

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   This type of PDT is less painful than conventional PDT. But because there is not as much research behind it, it is not used as often as conventional PDT.

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Photodynamic therapy was initially used to treat skin cancer. While that’s still its primary use, it’s also used to treat other types of cancers and conditions.

FDA-Approved Uses

PDT has been approved to treat the following conditions.

Actinic Keratoses (Precancerous Skin Lesions) PDT is approved for treating actinic keratoses, particularly on the face, scalp, and arms, says Aaron Farberg, MD, a double board-certified dermatologist who specializes in skin cancer, inflammatory diseases, and cosmetic dermatology at Bare Dermatology in Dallas.

Superficial Basal Cell Carcinoma (BCC) and Bowen’s Disease PTD is approved to treat superficial basal cell carcinoma and Bowen’s disease, also known as squamous cell carcinoma in situ, says Veena Vanchinathan, MD, a board-certified dermatologist in the Bay Area of California and a member of the American Academy of Dermatology.

“Photodynamic therapy is effective for these conditions because it selectively destroys abnormal cells while sparing healthy tissue,” says Dr. Vanchinathan.

Promising Off‑Label Uses

Research into off-label uses for PDT have found it to be effective for:

Rosacea and Other Skin Conditions “Some other less common, off-label uses for PDT include treating rosacea, photoaging of skin (skin changes due to sun damage), and warts,” says Vanchinathan.

Antimicrobial Uses for Infections “PDT is showing potential in wound healing and stimulating the body's immune response to fight diseases,” says Bruce Robinson, MD, a board-certified dermatologist in New York City.

PDT is a two-step process.

When this incubation period is complete, the treatment area will be exposed to a special blue or red light that activates the medicine. The light causes the photosensitizer to react and form an oxygen molecule that kills abnormal cells while minimizing damage to healthy tissue.

Before having PDT for skin cancer, you should tell your doctor about any over-the-counter (OTC) and prescription medications and supplements you take.

“Be prepared to discuss your medical history with your doctor, including any allergies or conditions that could affect the treatment or recovery,” says Dr. Robinson.

For example, people with a history of cold sores may need to take an antiviral beforehand to prevent a flare-up, he says. “Inform your doctor of any contraindications to PDT, such as pregnancy, lupus, porphyria, or hypersensitivity to the photosensitizer,” says Robinson.

If you use topical vitamin A products (like retinoids), stop taking them for a week before PDT, says Robinson.

To prepare for the procedure on the day of treatment, Robinson recommends:

• Clean your skin. 
Wash the treatment area thoroughly with soap and water and avoid applying any creams, lotions, or makeup.
• Shave (if needed). 
If you have thick, dense hair in the treatment area, shave it two days before the procedure. For facial treatment, men should shave the morning of the procedure.
• Bring sun protection. 
Bring sun-protective clothing, a wide-brimmed hat, and sunglasses to protect yourself from the sun on your way home.

During the light treatment, you may feel a tingling or burning sensation. If this becomes too painful, your doctor can turn off the light for a brief time to give you a break and then continue. Fans, ice packs, and medications can also help ease the pain.

• Stay indoors, especially for the first 48 hours after treatment.
• Avoid direct, bright, or strong indoor lights.
• Wear sunscreen, sun-protective clothing, and a hat when in natural sunlight.

You may want to apply a cool compress to the treated area for the first day to help ease any irritation or discomfort. You can also take OTC medications, such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), or aspirin. If your skin is itchy or you experience swelling, an antihistamine, such as Benadryl, may help.

The day after your treatment, use a gentle, fragrance-free cleanser to clean the treated area. Then, pat your skin dry with a clean towel. You might also want to apply a moisturizer to keep your skin hydrated. Keeping your moisturizer in the refrigerator can add a cooling effect.

Side effects after the treatment can include redness, peeling, crusting, swelling, and burning; all typically resolve in days to weeks, says Farberg. “Hyperpigmentation in darker skin tones may resolve over a few months, although in some cases it can be persistent.” Use sunscreen and avoid sun exposure afterward to reduce the risk, says Farberg.

Depending on the area that’s being treated, other side effects can include:

• Cough
• Trouble swallowing
• Stomach pain
• Painful breathing
• Shortness of breath

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• Photodynamic therapy is a versatile, targeted, minimally invasive treatment using a combination of photosensitizers and light.
• It’s FDA-approved for actinic keratoses, superficial skin cancers, certain types of cancer, and macular degeneration, with promising off-label uses.
• Darker skin tones may require special protocols to reduce hyperpigmentation risks.
• Side effects are generally mild, but pigment changes, reactions, or pain may occur.